Questions about Russia’s faltering military operation in Ukraine remain unanswered, as Kiev declared full control of the key eastern city of Lyman after Moscow’s troops withdrew.

It is Kyiv’s most significant battlefield victory in weeks, providing a potential staging point for increased eastward attacks while piling pressure on the Kremlin.

On Sunday, Ukrainian President Volodymyr Zelenskyy announced that his forces had taken control of Lyman after encircling it the day before.

“As of 12:30pm (09:30 GMT), Lyman has been fully cleared.” “Thank you to our armed forces, our warriors,” he said in a video message. Russia’s military made no comment on Lyman on Sunday, despite having announced the day before that it was withdrawing its forces from the area to move to “more advantageous positions.”

The loss of Lyman is a significant setback for Russian forces, who have relied on the city for months as a vital logistics and rail hub in the Donetsk region to transport military equipment, troops, and other supplies.

“Without those routes, it will be more difficult, so it presents a kind of quandary for the Russians going forward,” said US Defense Secretary Lloyd Austin.

Lyman is in the Donetsk region, near the border with the Luhansk region, and was recaptured by Ukraine by encircling Russian troops. These are two of the four regions or oblasts that Russia annexed on Friday after people voted in illegitimate referendums in Ukraine and the West.

The Institute for the Study of War, a think tank based in the United States, said Lyman’s death suggested Russia was “deprioritizing defending Luhansk” in order to keep occupied territory in southern Ukraine.

“Despite the recent collapse of the Kharkiv-Izyum front and even as Russian positions around Lyman collapsed, Ukrainian and Russian sources consistently indicate that Russian forces continued to reinforce Russian positions in Kherson and Zaporizhia oblasts,” it said.

On Sunday, the United Kingdom’s military described Lyman’s capture as a “significant political setback” for Moscow in a daily intelligence briefing. Taking the city allows Ukrainian troops to potentially advance further into Russian-occupied territory.

Ukraine’s capture of a city within President Vladimir Putin’s declared annexation territory shows that Ukrainians can push back Russian forces, according to NATO Secretary-General Jens Stoltenberg on Sunday.

“We’ve seen that they’ve been able to take a new town, Lyman, and that demonstrates that the Ukrainians are making progress, that they’re able to push back the Russian forces because of their courage, bravery, skills, but also, of course, because of the advanced weapons that the US and other allies are providing,” Stoltenberg said in an interview with American broadcaster NBC.

Ukrainian forces have retaken swaths of territory in recent weeks, most notably in the northeast around Kharkiv, in an offensive that has embarrassed the Kremlin and prompted rare domestic criticism of Putin’s war.

A pompous Kremlin annexation ceremony on Friday failed to quell internal Russian criticism of how its “special military operation” is being handled.

On Saturday, Putin ally Ramzan Kadyrov, the leader of Russia’s southern Chechnya region, called for a shift in strategy “all the way up to the declaration of martial law in border areas and the use of low-yield nuclear weapons.”

On social media, other hawkish Russian figures chastised Russian generals and Defense Minister Sergei Shoigu for failing to prevent the setbacks but stopped short of attacking Putin.