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.

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.

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

Ukrainian President Volodymyr Zelenskyy said he would be willing to withdraw troops from the country's eastern industrial heartland as part of a plan to end Russia's war, if Moscow also pulls back and the area becomes a demilitarized zone monitored by international forces.

On December 18, Russian commander-in-chief Valery Gerasimov gave an end-of-year report to foreign military officials, claiming Russia seized 6,300sq km (2,432sq miles) of Ukraine this year, slightly more than the 6,000sq km (2,300sq miles) Russian Defence Minister Andrei Belousov had claimed a week earlier.