LONDON: Tens of thousands of Ukrainian troops who smashed into Russia last summer and took control of a swathe of territory there are nearly encircled by Russian forces and cut off from their main supply lines, open source maps showed on Friday.

Ukraine`s situation in Russia`s Kursk region has deteriorated sharply in the last three days, the same maps show, after Russian forces retook territory as part of a gathering counteroffensive that has nearly cut the Ukrainian force in two.

The precarious situation for Ukraine raises the possibility that its forces may be forced into a politically awkward and psychologically difficult retreat back into Ukraine, or risk being captured or killed at a time when Kyiv is under mounting pressure from the US to agree a ceasefire with Russia.

`The situation (for Ukraine) is very bad,` Pasi Paroinen, a military analyst with the Finland-based Black Bird Group, said.

`Now there is not muchleft until Ukrainian forces will either be encircled or forced to withdraw. And withdrawal would mean running a dangerous gauntlet, where the forces would be constantly threatened by Russian drones and artillery,` he said.

`If Ukrainian forces are not able to restore the situation quickly, this could be the moment where the Kursk salient begins to finally close into an encircled pocket.

There was no official confirmation of the Russian thrust from the defence ministry in Moscow or the Ukrainian military, both of which tend to report battlefield changes with a delay.

Taking the war to Russia Ukraine`s incursion into Kursk last August was the most serious attack on Russian territory since the Nazi invasion of the Soviet Union in 1941 and was designed to bring the war to ordinary Russians, whom the Kremlin had tried to shield from the fallout from the fighting raging inside Ukraine.-Reuters