Russia said it has withdrawn its troops from the once-occupied city of Lyman, as Ukraine’s eastern counter-offensive recaptures more territory.
The announcement came through the Tass and RIA news agencies, citing the Russian defence ministry.
Lyman is 100 miles south-east of Kharkiv, Ukraine’s second-largest city.
Ukrainian forces had pushed across the Oskil River as part of a counter-offensive that saw Kyiv retake vast swathes of territory beginning in September.
Lyman, a key transportation hub, had been an important site in the Russian front line for both ground communications and logistics.
With that barrier overcome, Ukraine can potentially push further into the occupied Luhansk region, which is one of four regions that Russia annexed on Friday after an internationally criticised referendum vote at gunpoint.
The fighting comes at a pivotal moment in Russian President Vladimir Putin’s war.
Facing Ukrainian gains on the battlefield – which he frames as a US-orchestrated effort to destroy Russia – Mr Putin this week heightened his threats of nuclear force and used his most aggressive, anti-Western rhetoric to date.
Russia’s defence ministry claimed to have inflicted damage on Ukrainian forces in battling to hold onto Lyman, but said outnumbered Russian troops were withdrawn to more favourable positions.
The Russian announcement came soon after Ukraine’s air force said it had moved into Lyman and the Ukrainian president’s chief of staff posted photos of a Ukrainian flag being hoisted on the town’s outskirts.
Lyman is in the Donetsk region near the border with Luhansk, both of which Russia annexed on Friday after the widely-criticised “referendum vote”.
Meanwhile, Russian bombardments have intensified in recent days as Moscow moved swiftly with the annexation and ordered a mass mobilisation at home to bolster its forces.
In the north-east, Ukrainian officials accused Russian forces of attacking a civilian evacuation convoy, killing 20 people including children.
In the south, Ukraine’s nuclear power provider said on Saturday that Russian forces had blindfolded and detained the head of Europe’s largest nuclear plant.
Despite Mr Putin’s land-grab Friday of four regions, Ukrainian President Volodymyr Zelensky and his military have vowed to keep on fighting to liberate the annexed regions and other Russian-occupied areas.
Ukrainian authorities also accused Russian forces of targeting two humanitarian convoys in recent days, killing dozens of civilians.
The governor of the Kharkiv region, Oleh Syniehubov, said 24 civilians were killed in an attack earlier this week on a convoy of people trying to flee the Kupiansk district, calling it “сruelty that can’t be justified”. He said 13 children and a pregnant woman were among the dead.
“The Russians fired at civilians almost at point-blank range,” Mr Syniehubov wrote on the messaging app Telegram.
The Security Service of Ukraine, the secret police force known by the acronym SBU, posted photographs of the attacked convoy.
At least one truck appeared to have been blown up, with burned corpses in what remained of its truck bed. Another vehicle at the front of the convoy also had been ablaze.
Bodies lay on the side of the road or still inside their vehicles, which appeared pockmarked with bullet holes.
Russia’s defence ministry said its rockets destroyed Ukrainian military targets in the area, but has not commented on accusations that it targeted fleeing civilians.
Russian troops have retreated from much of the Kharkiv region amid the successful Ukrainian counter-offensive, but have continued to shell the area.
In its heaviest barrage in weeks, Russia’s military on Friday pounded Ukrainian cities with missiles, rockets and suicide drones, with one strike in the Zaporizhzhia region’s capital killing 30 people and wounding 88.
The UK’s Ministry of Defence said the Russians “almost certainly” struck a humanitarian convoy there with S-300 anti-aircraft missiles. Russian-installed officials in Zaporizhzhia blamed Ukrainian forces, but gave no evidence for this.
In other fighting reported on Saturday, four people were killed and six wounded by Russian shelling Friday in the Donetsk region, governor Pavlo Kyrylenko reported.
The Russian army struck the southern Ukrainian city of Mykolaiv twice overnight, once with drones and the second time with missiles, according to regional governor Vitaliy Kim. Five people were injured, including a three-month-old baby, he said.
After Friday’s land grab, Russia now claims sovereignty over 15% of Ukraine, in what Nato Secretary-General Jens Stoltenberg called “the largest attempted annexation of European territory by force since the Second World War”. He added that the war is at ”a pivotal moment”.
On Friday, Mr Zelensky formally applied for Nato membership, upping the pressure on Western allies to defend Ukraine.
In Washington, US President Joe Biden signed a bill on Friday that provides another infusion of military and economic aid to Ukraine.