KABUL, Afghanistan — Inside the 25-foot-high, barbed-wire-topped walls of Pul-e-Charkhi prison, a thin line divides the Taliban of the past and what the militants claim they have become.

To Afghanistan’s new rulers, the inmates are evidence of their ability to effectively police the capital in a law-abiding manner. But on a recent day, when scores of prisoners gathered outside their cells to soak in the sun, some said they were arrested on flimsy accusations. Others described being treated violently, reminiscent of the harsh justice doled out by the militants when they ruled in mid-1990s. None of the inmates had lawyers.

“They beat me up badly,” said Haji Hussein, a taxi driver who said he was arrested at a Taliban checkpoint because two of his passengers were drunk.

“My son killed a person and escaped, but they put me in jail instead,” said Timur Shah, speaking from behind a chain-link fence.

In the vacuum left by the sudden fall of the U.S.-backed Afghan government, the Taliban have stepped in to provide much-needed security to Kabul and other cities.

Long-haired, bearded militants oversee checkpoints to net criminals. District police chiefs, mostly commanders from the al-Qaida-linked Haqqani network, solve local disagreements. Community judges informally deliver verdicts on land, money and family disputes, as the militants have done for years in rural areas.

But transforming a village-based guerrilla insurgency — accustomed to war for the past two decades — into a national security force capable of protecting vulnerable urban areas is proving challenging for the militants.

The Islamic State-Khorasan, the Syria- and Iraq-based terrorist group’s branch in Afghanistan and Pakistan, has emerged as the most significant threat to the Taliban’s dominion as well as to public safety. So far, the Taliban have failed to contain the terrorists, who have staged numerous attacks nationwide since the militants’ takeover of the country two months ago, including two bombings of Shiite mosques within a week in Kandahar and Kunduz that killed scores of worshipers. That raises questions about whether the Taliban have the appropriate expertise, training and intelligence capabilities to take down ISIS-K cells in Kabul and other urban areas, despite orchestrating similar assaults before the group overran the country.

Inside the Taliban’s own ranks, many fighters remain undisciplined and have committed crimes. People are often sent to prison on the slightest suspicion of illegal activity. They have no legal counsel and are languishing in cells until a formal judicial system is put in place.

As he listened to the grievances of his prisoners, Qari Zaki, a Taliban prison official, laughed, even as he acknowledged the questionable tactics.

“Who will accept the crimes they commit?” he said. “Everyone believes they are innocent. The people made complaints about them, so we captured them.”

The militants are also showing signs of a return to the brutal methods they used to impose order under their previous rule. In the western city of Herat, fighters have executed suspected kidnappers and hung their bodies on tall cranes in public view. Videos of Taliban fighters whipping alleged criminals have emerged on social media.

Even in the capital, where the world’s spotlight is on the militants, reports have emerged of accused thieves being paraded in public, their faces smeared with black grease. One captured narcotics dealer had his product stuffed into his mouth and his picture posted on social media as a warning.

In interviews around Kabul, police chiefs and fighters openly said they want their leadership to impose the kinds of strict Islamic punishments that were in place from 1996 to 2001, until the Taliban were ousted following the Sept. 11 attacks. All supported the hangings in Herat.

“If a court decides to cut the hand of a thief, we will support it,” said Qari Mohammed Ashraf, 43, the police chief of the capital’s District 12. “God willing, the punishment will be carried out publicly. The people will learn from it, and the thieves will stop thefts. And God willing, if a married woman commits adultery, she shall be stoned to death in public.”

Ashraf acknowledged that it was his men who nabbed the dealer.

“We sent a message by putting the drugs in the mouth of a seller,” he said. “If anyone does such things, he will face the same punishment.”

For now, the Taliban have more pressing concerns. Maulavi Zubair Mutmaen understands.

Burly with a black beard that matches his turban, he is in charge of Kabul’s District 9, the largest police district in the country, which makes him quite possibly the city’s most powerful law enforcer.

His experience, he said, comes from controlling a large area in the mountains of Logar province with “three fighters” and a network of informants. He was also a member of a Taliban shadow military commission that oversaw the capital during the previous government, he said, adding that other shadow commissions dealt with courts, prisons and other aspects of governance.

“We had a complete government set up before taking control of Kabul,” said Mutmaen, smiling. The main difference now, he said, is that urban people feel “using alcohol is democratic, adultery is democratic, and robbing and kidnapping are their rights under the previous regime.”

“It will take time to bring these people back to normal life,” he added.

Among his fighters are some who know Kabul from an alternate angle: They were Taliban spies in the capital for years.

But Mutmaen’s tenure so far has been marked by failure in one particular area: stopping the Islamic State-Khorasan.

It was his fighters who were securing Kabul’s airport in the waning days of the American military withdrawal when an ISIS-K suicide bomber killed 13 U.S. service members and at least 170 Afghans.

Since then, Taliban commanders and fighters say they have been hunting for ISIS-K cells. Ashraf, the District 12 police chief, said his men recently captured six suspected terrorists in a night raid, based on their intelligence gathering. In August, shortly after the airport bombing, a senior Taliban commander said the militants were monitoring phone calls, emails and other forms of communication to combat ISIS-K.

But it’s unclear how much coordination exists among police districts in a capital where Taliban fighters have come from different parts of the country, each beholden to their immediate commanders, allowing ISIS-K to stage attacks easily. The U.S. military, the CIA and their Afghan counterparts also found it difficult to prevent suicide bombings and other urban attacks by both the Taliban and ISIS-K.

Adding to the obstacles is a sense of denial. Ashraf said that ISIS-K poses “no major threat.” And Mutmaen said the threat has “been reduced.” He also blamed American troops for the airport attack, saying the explosion occurred on the U.S. side of the gate.

Five days after the interview, ISIS-K claimed responsibility for a bombing outside a mosque in Kabul that killed at least five civilians; it happened during a memorial service for the mother of the Taliban’s acting deputy information minister.

On the night of Oct. 5, Ashraf’s forces were on the hunt for a notorious criminal kingpin named Mustafa. A Taliban national security intelligence team had traced his cellphone but was able to track his whereabouts only to the general vicinity of a neighborhood, said Murtaza Ahmadzai, a Taliban police official.

So his units erected eight checkpoints in the area, hoping to find Mustafa through a search of passing vehicles.

“We have our own way of intelligence,” Ahmadzai said.

He nodded toward nearby stores with lights on.

“Ask anyone here how great the security is now,” he said. “In the previous government those shops would be closed at this time.”

During the Taliban’s previous rule, many Afghans initially embraced the militants for bringing law and order after years under the grip of corrupt warlords and their militias. Improving security is again paramount to establishing the Taliban’s legitimacy, and to convincing foreign powers, donors and potential investors that it has changed and can run a government based on the rule of law.

“This is the biggest test from Allah, to serve the people and resolve the problems of the people,” said Ibrahim Haideri, a Taliban fighter, minutes after arresting two men for selling fake visas to Tajikistan in another area of the capital.

On the surface, at least, many Afghans have welcomed the newfound security. Under the previous government, robberies, kidnappings and other crimes, aided by corrupt police departments and local officials, plagued the capital and ripped its social fabric. Now, the night is no longer as fearsome, many Kabul residents said in interviews.

“We would avoid going out after 7 p.m.,” said Sayed Razak, a shopkeeper. “There were a lot of robberies, kidnappings and killings. But it’s better now.”

Others painted a more complex picture.

“There are a lot of people with weapons now,” said Mohammed Sadeq, a grocery store owner. “We’ve heard a lot of reports of robbers entering homes and taking things. They don’t wear formal uniforms. We don’t know who they are.”

Many are Taliban fighters. Senior commanders acknowledge cases of bad behavior and say there have been consequences. At least 60 militants are being held in a section of Pul-e-Charkhi prison for crimes such as raiding homes at night and robbery, said a Taliban prison official who spoke on the condition of anonymity because he wasn’t authorized to talk to journalists. A second prison official confirmed that there were Taliban inmates but did not know how many.

Mutmaen, the District 9 police chief, said that there have been cases in which police officers “misused their powers” and that some officers were removed from their posts. They include fighters who took the law into their hands, he added, such as by publicly shaming suspected criminals.

“There are some scattered incidents of blackfacing by a mujahid, but this is not the policy of the leadership,” said Mutmaen, using a word for a Taliban fighter. “This may have been the mujahid’s personal decision.”

Taliban police chiefs are also facing high expectations to address the wrongs of the past. On a recent day, dozens of Afghans waited to meet Ashraf in his spacious office, a ritual that occurs every day in virtually every police district.

They hoped he could resolve disputes within their communities or with neighbors that had lasted for years, including arguments over money and over land. Some had languished in the former government’s courts; others remained unresolved because of official graft, said some plaintiffs.

Ashraf, who also served on the Taliban’s shadow military council, said the militants held similar sessions in areas they controlled over the past 20 years. “The previous regime could not solve the problems of the people as there was corruption and influence peddling,” he said. “We decided cases through a swift justice system. Therefore, the people preferred to come to us.”

He listened patiently to a years-old dispute over water. A man explained that he had dug a well about 100 feet into the ground, deeper than those around him. So the neighbors complained that he was getting all the water. Both sides were in his office. It was up to Ashraf to make a decision. He said he would have an answer for them in a few days.

In another part of the city, the future of Afghanistan’s jurisprudence was on display.

The district police chief had sent a dispute between a husband and wife to an informal community court, similar to what the militants convened in their mountain villages.

Two Taliban religious legal scholars sat on red floor cushions in a small office. Addressing them, the wife, Kamila, explained that for the past five months she had been living in fear of her husband, Ali. He had beaten her several times, and denied her food and medication. She was five months’ pregnant.

Now, she wanted a divorce.

Without evidence, Ali accused her of stealing jewelry. He said she always wanted to visit her mother’s home, over his objections. But he refused to agree to a divorce.

It was immediately clear whom the judges favored.

“In Islamic sharia law, a wife always listens to her husband,” said one judge. “If he says you can’t go to your mother’s house, you should not go.”

They declined her request. In their interpretation, only her husband could divorce her.

“Nobody wants to destroy her life with an unborn baby,” said Kamila, a pained look sweeping across her face. “But I cannot go to him. He can either keep the baby, or I will raise my kid myself.

“Multiple times, he pointed a gun at me and threatened to kill me.”

Calling her “rebellious,” one judge said that if “she refused to accept the decision of the Islamic emirate and your husband,” she would be publicly ostracized as a nonbeliever of sharia.

Then the judges ordered the pair to go outside and work out their problems.

The Taliban head of the Pul-e-Charkhi prison also has a glimpse of the future. And he’s worried.

As the militants seek to establish security in the capital, more Afghans accused of crimes are arriving at the facility to await trial when the courts are created. But employees haven’t been paid their salaries in two months or longer. Many have quit, leaving the prison short-staffed.

“We are asking them to return to their jobs,” said Maulavi Abdullah Haqeeq, the director. “God willing, they will get salaries.”

One future inmate, though, has yet to arrive.

As of Friday, the Taliban police had not captured Mustafa, the robber kingpin.

The Washington Post’s Haq Nawaz Khan in Peshawar and Ezzatullah Mehrdad in Islamabad, Pakistan, and Mohammadullah Aryen in Kabul contributed to this report.