Ukraine forces are navigating giant minefields and mounting initial attacks on Russian positions along a sprawling front line, U.S. and Ukrainian officials said, as Kyiv takes the first, halting steps of what is expected to be a prolonged and punishing counteroffensive campaign.

Ukrainian officials say they have thus far reclaimed at least 130 square kilometers, or about 50 square miles, in the country’s south from Russian forces, which have spent months hardening fortifications and positioning reinforcements in their bid to protect territory seized since President Vladimir Putin’s 2022 invasion.

President Volodymyr Zelensky last week said that the offensive was moving “slower than desired” since it began this month, but that an operation against an adversary with a deeper arsenal and a far larger force shouldn’t be expected to unfold at an action-movie pace.

A U.S. military official, who spoke on the condition of anonymity to discuss sensitive battlefield assessments, said Ukraine’s military was now “fighting through the initial security zone” before hurling the bulk of its manpower at Russia’s main lines.

“You don’t commit your whole force until you have an idea of where the areas are where you’re going to find the most success,” the official said. “The Ukrainians have to figure out where the Russian defenses are the weakest and most porous.”

The operation is unfolding as Western officials are assessing the fallout of the stunning weekend rebellion by mercenary leader Yevgeniy Prigozhin, whose forces have played a key role in expanding Russia’s combat power in Ukraine. The incident underscored the deep strains the war has caused within Russia and injected a new element of unpredictability into the conflict’s course.

American officials caution against drawing conclusions in the offensive’s early weeks and say the absence of traditional offensive moves — akin to the advancing armored columns of World War II — does not indicate trouble but rather a new sort of 21st-century maneuver warfare, one that has included probing strikes, sabotage attacks behind enemy lines, and artillery and missile strikes deep into Russian-held areas.

But the recaptured areas, which Ukrainian officials say include at least a half-dozen villages near the borders of the eastern Donetsk and Zaporizhzhia regions, represent a tiny fraction of the vast area the Kremlin controls, which still amounts to roughly a fifth of the country.

The limited scale of the gains to date is a reminder of the challenges Zelensky faces in his effort to force Putin to reconsider his desire to cement control over much of Ukraine. The Russian leader has sought to sow doubts about Ukraine’s battlefield prowess, arguing without evidence that Kyiv has suffered losses exponentially greater than Russia’s and that much of its Western-donated weaponry has already been destroyed.

“Everything with which they fight and everything that they use is brought in from the outside,” he told the St. Petersburg International Economic Forum in recent days. “You can’t fight for long like that.”

Putin has claimed that Western tanks, including German-donated Leopards, have been destroyed and that Ukraine has lost 923 tanks and armored vehicles since June 4. He vowed that F-16 fighter jets, which some European nations are now working to supply, “will also burn, there is no doubt.”

Throughout the war, neither government has provided a reliable accounting of its combat casualties, though U.S. assessments revealed earlier this year suggest that those figures are astronomical.

In areas north of the war-scarred city of Bakhmut, Russian forces are attempting their own offensive thrusts, which a senior Ukrainian official said were blocked this week, even as the Kremlin continues its regular standoff strikes on Ukrainian cities.

Despite Putin’s warnings, Ukraine’s backers in the West are continuing to supply Ukraine with an expanding array of weapons, including British Storm Shadow cruise missiles, which have increased Kyiv’s reach into Russian-held territory. On Tuesday, the Biden administration said it was sending an additional $500 million in military aid, including dozens of armored vehicles to augment or replace those damaged or destroyed.

Military experts say Ukrainian forces have focused their efforts to inflict Russian losses in three main areas, including Orikhiv in the Zaporizhzhia region and Velyka Novosilka and Bakhmut in Donetsk, in an attempt to break through toward areas that could split the occupied Crimea region from other Russian-held territory. So far they appear to have committed only some of the new brigades created to boost Ukraine’s odds in the fight, keeping other units in reserve so they can be employed as an exploitation force if breakthroughs occur.

Privately, U.S. military officials concede that their expectation from early this year, described in leaked intelligence documents, that Ukraine is likely to make only modest gains in its counteroffensive has not changed, despite public pronouncements seeking to downplay fallout from the disclosure. But administration officials also argue that even a modest advance could illustrate to Russian elites — and potentially to Putin himself — that hopes for expanding Russia’s grip are futile.

Rob Lee, who served as a U.S. Marine infantry officer and is now a fellow at the Foreign Policy Research Institute, said this fight will be different from Ukraine’s successful counteroffensive last fall, in part because now Russia is taking the prospect of an Ukrainian offense more seriously than it did before Ukraine’s recapture of Kharkiv and because it will be easier for Russia to resupply front-line troops now than it was last year in the city of Kherson, on the west bank of the Dnieper River. This time, Russia had time to create formidable defenses and bring in more drone aircraft.

Lee said that resources, not time, ultimately will determine who prevails. “If Ukraine can afflict enough attrition, if they can isolate the objective, prevent reinforcements from arriving, supplies, you can still maybe achieve a breakthrough,” he said. “And that could lead to kind of success.”

An initial obstacle for Ukraine’s military leadership is the sheer scope of the 600-mile front line, meaning Kyiv has had to thin out and disperse its limited force. Ukrainian officials say that Russia has positioned up to 360,000 troops inside Ukraine and that, unlike last fall when Kyiv was able to retake major cities in a two-pronged push, Russia has had time to build up three or four layers of defenses including trenches and other fortifications.

Another challenge is the heavily mined areas that constitute an outer layer of Russian defenses. Ukrainian officials say the territory mined by Russia covers more than 77,000 square miles. Pentagon officials expect Ukrainian forces to eventually push through them. “Minefields don’t beat an offense; they slow an offense,” the U.S. military official said.

Ukraine also lacks both air superiority and the 3-to-1 offensive to defensive troop ratio that Western militaries typically want for this kind of push. Ukrainian officials say Russian helicopters and fixed-wing aircraft give the Kremlin another advantage along the line of contact.

Mykhailo Podolyak, an adviser to Zelensky, said Ukrainian forces are seeking creative solutions to those problems even as they intensify shelling of Russian logistics and staging facilities behind the front lines.

“I understand that sometimes the word ‘counteroffensive’ means a ‘blitzkrieg’ — they started in the morning and finished in the evening,” he told The Washington Post. “But it is not.”

Podolyak said the current objective is to determine Russian vulnerabilities, weaken their defenses and make “thoughtful” use of resources. “That is why we say that this stage is difficult and requires a more patient attitude. Including from observers,” he said. He noted that the incremental pace of outside arms supplies had also shaped the operation’s speed.

One Ukrainian soldier near Velyka Novosilka, who asked to be identified by his call sign, Mansur, said he believes the campaign will be more difficult in Donetsk than it has been elsewhere. Unlike in other areas, Russian troops have had years to fortify positions and build support from local residents. “It motivates the enemy more,” he said. “This area will be tougher.”

Pressure is growing on the Biden administration to provide Ukraine more sophisticated weaponry, including the Army Tactical Missile System (ATACMS), which would allow Ukraine to conduct more strikes deep in Russian-held areas. Last week, the House Foreign Affairs Committee passed a resolution calling for the missiles to be provided.

William Taylor, who served twice as the top U.S. diplomat in Kyiv, said Ukraine has a chance to recover all occupied territory if it gets the right supplies. “A lot depends on what we provide them,” said Taylor, who is now retired from government service and serves as vice president for Europe and Russia at the U.S. Institute of Peace. “We can affect the probabilities.”

Another Ukrainian soldier who commands a National Guard unit in the Donetsk region said he feels the weight of expectations from his fellow Ukrainians.

The soldier, who goes by the call sign Hephaestus, for the Greek god of fire, said the fighting in the Donetsk and Luhansk regions is complicated by terrain that includes vast swamps and forests, making assault operations more difficult. But he said Ukraine’s military leadership was determined to calibrate its battle plans to avoid unnecessary losses in its ranks.

“We understand that we are not using Soviet methods,” he said. “The priority for us is every human life.”

Without a careful, measured approach to the campaign, he said, “there will be unjustifiably immense sacrifices.”

Stern reported from Kyiv, and Dixon reported from Riga, Latvia. The Washington Post’s Samantha Schmidt in Ukraine’s Donetsk region and Francesca Ebel in Kramatorsk, Ukraine, contributed to this report.

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