The eastern Ukrainian city of Lyman was retaken from occupying forces on Saturday, one day after Vladimir Putin declared the region to be part of Russia.
After being encircled by Ukrainian troops, Moscow pulled its forces out of the metropolis it had been using as a front-line hub. It was the latest victory for the Ukrainian counteroffensive that has humiliated and angered the Kremlin.
Russia’s withdrawal from Lyman complicates its internationally vilified declaration just a day earlier that it had annexed four regions of Ukraine — an area that includes Lyman.
Taking the city paves the way for Ukrainian troops to potentially push farther into land that Moscow now claims as its own.
Russia had 5,000 to 5,500 troops at Lyman but their numbers may have been lower because of casualties and soldiers trying unsuccessfully to break out, a representative of Ukraine's eastern forces claimed.
Russia has used Lyman as a logistics and transport hub for its operations in the north of the Donetsk region. Its fall would be Ukraine's biggest battlefield gain since a lightning counteroffensive in the north-eastern Kharkiv region last month.
Serhii Cherevatyi said the capture of Lyman would allow Ukrainian forces to advance into the Luhansk region, whose full capture Moscow announced at the beginning of July after weeks of slow, grinding advances.
“Lyman is important because it is the next step towards the liberation of the Ukrainian Donbas. It is an opportunity to go further to Kreminna and Severodonetsk, and it is psychologically very important,” he said.
The operation around Lyman is still under way and Russian troops are mounting unsuccessful attempts to break out of the encirclement, Mr Cherevatyi said.
“Some are surrendering. They have a lot of killed and wounded, but the operation is not yet over,” he said.
Ukraine's exiled governor of Luhansk said Russian forces had sought safe passage out of the encirclement, but Ukraine rejected the request.
The Ukrainian General Staff said it had no such information.
Mr Putin proclaimed the Donbas regions of Donetsk and Luhansk and the southern regions of Kherson and Zaporizhzhia to be Russian land in Friday's ceremony — a swathe of territory equal to about 18 per cent of Ukraine's total surface land area.
Ukraine and its western allies said the annexation was illegal. Kyiv vowed to continue liberating its land of Russian forces and said it would not hold peace talks with Moscow while Mr Putin was president.
Vladimir Putin announces annexation of four regions of Ukraine - in pictures
