Ukraine said a resistance agent was able to sneak into a Russian hangar and destroy two Russian fighter jets.

Kremlin is analysing the documents on ending the war in Ukraine which were brought to Moscow by special envoy Kirill Dmitriev from the United States, Kremlin spokesman Dmitry Peskov said on Thursday.

The vessel is part of Russia's so-called "shadow fleet" - unregulated ships that Kyiv says are exporting large quantities of oil despite Western sanctions.

Russia has ordered a winter troop surge to break the stalemate in Ukraine, but Ukrainian drone attacks on logistics and resupply channels will undermine this offensive.

Ukraine has tried to evacuate areas of Sumy region near the Russian border, but many civilians have refused to leave.

Ukrainian security services have stepped up drone and sabotage operations against Russian combat aircraft and submarines this month, in what analysts see as one way to combat incessant Russian missile strikes against cities and energy infrastructure.

The recapture of the eastern city will come as a humiliating blow to Vladimir Putin and his army high command.

Ukrainian forces say they have hit an oil terminal, a pipeline, two parked jet fighters, and two ships in a series of strikes on Russian soil