The fight against Islamist insurgents in Africa may have suffered a significant blow Thursday when army officers in the West African country of Niger said they were supporting the leaders of a coup against the president, a key ally of the United States and other Western governments.

Nigerien President Mohamed Bazoum was detained a day earlier by soldiers, who declared on national television that they had overthrown him. Even as Bazoum said on Twitter that his rule would be "protected" by democracy-loving patriots, the army and various law enforcement agencies coalesced Thursday behind the Presidential Guard, which led the coup. The army said it was backing the coup leaders to avoid bloodshed.

Bazoum, who was democratically elected, and his predecessor had worked closely with the United States, France and other Western countries in confronting a mounting threat by Islamist militants. The United States has stationed about 800 soldiers in Niger, operates drones from a large base in the city of Agadez and trains Nigerien soldiers.

A military spokesman for the U.S. Africa Command said it was "too soon to speculate on any potential future actions or activities" in Niger. The French military, which has worked especially closely with the Nigeriens after leaving Burkina Faso and Mali following coups in those countries, declined to comment.

If the U.S. government declares the takeover in Niger a coup - which Secretary of State Antony Blinken said Wednesday was for lawyers to determine - the law stipulates that direct military aid must be suspended. That would raise questions about whether the French and other Western countries would also sever their partnerships with Niger, said Andrew Lebovich, a research fellow with the Clingendael Institute, a think tank in the Netherlands.

"It could fit into a narrative that the Malian and Burkinabe governments have used of saying, 'Our traditional security partners have abandoned us in our time of need, and so they are no longer good partners,'" said Lebovich. "And that could further complicate an already tenuous situation."

If the military takeover holds, there will be an unbroken string of countries in sub-Saharan Africa, stretching from the Atlantic Ocean to the Red Sea, led by juntas that have seized power in coups.

A senior U.S. official in Washington said Thursday that it is extremely difficult to predict what will happen next in Niger. Bazoum, the official said, assumed some risk at home by allowing the U.S. military to pursue armed militants in his country. As a result, some people would be happy to see him gone.

Rahmane Idrissa, a Nigerien political scientist based in the Netherlands, said it remains unclear what impact a Western withdrawal from Niger would have on security, partly because it is difficult to assess what those partnerships have achieved. Fatalities in Niger linked to extremists are down this year compared with last, according to data compiled by the Africa Center for Strategic Studies, but the country still faces violence along its borders. Neighboring Burkina Faso and Mali confront a security crisis.

"We have not seen much progress in the fight," Idrissa said. "But maybe the progress is coming from things we cannot see, and we will realize only when it is gone and say, 'Oh, that is why they were here.'"

In Mali and Burkina Faso, violence has worsened since the most recent coups, in 2021 and 2022, respectively. Extrajudicial killings and enforced disappearances by Islamist groups linked to the Islamic State and al-Qaeda have increased. So have violent crackdowns by both countries' armies, which have been accused of killing civilians. Mali's government has welcomed the Russian paramilitary Wagner Group, which was implicated in a massacre of more than 300 civilians last year.

Idrissa said the Nigerien military, which he described as more pragmatic and less ideological than those in Mali and Burkina Faso, is portraying the coup leaders as technocrats who will focus not on politics but strictly on security. But he noted that some of the coup leaders were in Bazoum's government, so it is unclear what they would do differently now.

Ulf Laessing, director of the Regional Sahel Program at the Konrad Adenauer Foundation in Mali, said the coup leaders will probably be focused on "consolidating power after their putsch" and less supportive of international security efforts in Africa's Sahel region. He noted that the Nigerien army, with Western help, had been making some progress in containing the regional Islamist threat.

Blinken said Wednesday that the United States' "own strong economic and security partnership with Niger depends on democratic governance and respect for the rule of law."

France's Foreign Ministry did not respond to questions about whether the French partnership would continue if the coup holds. But the ministry said in a statement that it strongly condemns the coup, calls for the release of Bazoum and his family, and supports "regional efforts to find an urgent way out of the crisis that respects Niger's democratic framework and enables the immediate restoration of civilian authority."

At the Russia-Africa summit underway in St. Petersburg, the Niger coup was being "very actively discussed," according to Kremlin spokesman Dmitry Peskov. Wagner-affiliated Telegram channels on Thursday cheered the coup in Niger as an opportunity to extend the group's influence in the Sahel by fostering ties with the new military leadership.

"What happened in Niger is the struggle of the people of Niger against the colonizers, colonizers who impose their rules of life, their conditions and keep them in a state that was in Africa hundreds of years ago," Wagner leader Yevgeniy Prigozhin said on Telegram. "Today it is actually gaining independence and getting rid of the colonizers."

John Lechner, a researcher focused on Wagner in Africa, noted that he has seen no evidence that Russia or Wagner was directly involved in the coup, but he said it is inevitable that both pro- and anti-Russian forces will try to use the situation to advance their own agendas.

Although some supporters of the coup have express pro-Russian sentiments and linked Bazoum with France, Lechner noted that the coup in Burkina Faso, where leaders have for months rejected advances by Wagner, indicates that the group's presence "doesn't spread like a virus."

"At the end of the day, governments have to agree to Wagner coming," he said. "They don't just arrive."

In the Nigerien capital, Niamey, demonstrators burned and ransacked the headquarters of Bazoum's party on Thursday. But hundreds of others turned out to protest in favor of democracy, and were shot at with live fire by the army, according to the Associated Press.

Dijé Hassane, a 38-year-old housewife, said that instead of carrying out a coup, "the military should go fight the terrorists."

"I heard some people rejoicing, but they don't know military regimes," she said. "They will not do better than Bazoum. . . . They are going to take us back 30 years, jeopardizing everything done so far."

Ousseini Hamza, a 33-year-old taxi driver, said he learned of the coup when a customer informed him. He said he believes that the military will follow in the path of Burkina Faso and Mali and "chase France out to fully exercise their sovereignty."

"As France has its say in our countries, we will have problems," he said, blaming the former colonial power for taking the riches of uranium-rich Niger. "Bazoum is a great friend of France, so he will let them do as they wish in Niger. The military in the contrary will probably seek the help of Russia to fight the terrorists like in Mali and Burkina Faso."

The Washington Post's Issa Ly Hamidou in Niamey, Robyn Dixon in Latvia, Michael Birnbaum in Wellington, New Zealand, and Dan Lamothe in Washington contributed to this report.