Russia says Ukraine has launched a new attack in the western Kursk region, from which Russian troops have been trying to eject Ukrainian forces for the past five months.

Ukrainian troops broke across the border in a surprise incursion on August 6 and have managed to hold on to a chunk of territory there which could provide Kyiv with an important bargaining chip in potential peace talks.

Russia's defence ministry said its forces were beating back the Ukrainian forces but some reports from Russian military bloggers suggested the Russian side had come under heavy pressure.

Andriy Yermak, the head of Ukrainian President Volodymyr Zelenskiy's office, posted on Telegram that there was "good news" from Kursk, adding: "Russia is getting what it deserves".

Andriy Kovalenko, the head of Ukraine's official Centre Against Disinformation, wrote on Telegram that Russian troops were attacked in several places on Sunday.

The Russian statement said Ukraine attacked in the early hours near the village of Berdin with two tanks, a mine-clearing vehicle and 12 armoured combat vehicles with paratroops.

"Artillery and aviation of the North group of (Russian) forces defeated the assault group of the Ukrainian Armed Forces," it added.

The statement said two Ukrainian attacks had been repelled. Reuters could not independently verify the situation on the ground.

Reports from Russia's widely read war bloggers, who support Moscow's war in Ukraine but have often reported critically on failings and setbacks, indicated that the Ukrainian assault had put Russian forces at least temporarily on the defensive.

"Despite strong pressure from the enemy, our units are heroically holding the line," the Operativnye Svodki (Operational Reports) channel said in the first hours after the attack.

In a later update, another influential blogger, Yuri Podolyak, said Russian units had gained control of the situation after initial "mistakes" and encircled Ukrainian forces north of a highway leading to the regional capital Kursk.

Acting Kursk governor Alexander Khinshtein told people to trust only official sources, and warned displaced residents not to return to unsafe areas without permission.

Ukrainian and Western assessments say that some 11,000 troops from Russia's ally North Korea have been deployed in the Kursk region to support Moscow's forces. Russia has neither confirmed nor denied their presence.

Ukrainian President Volodymyr Zelenskiy said on Saturday: "In battles yesterday and today near just one village, Makhnovka, in Kursk region, the Russian army lost up to a battalion of North Korean infantry soldiers and Russian paratroops."

He did not provide specific details. A battalion can vary in size but is generally made up of several hundred troops.

Russian President Vladimir Putin said in response to a question at his marathon annual phone-in last month that Russia would definitely drive Ukrainian forces out of Kursk but declined to set a date for when this would happen.

Russia currently controls about a fifth of Ukraine, but Ukraine's unexpected success in biting off and retaining a slice of Russian territory could boost its negotiating position as both sides gear up for possible peace talks this year.

Both have been striving to improve their battlefield positions before US President-elect Donald Trump is sworn in on January 20. Trump has repeatedly said he will bring a quick end to the war, but without saying how.

By committing some of its most effective units to the Kursk offensive, Ukraine has, however, weakened the defence of its own eastern regions where Russian forces have advanced since August at their most rapid pace since 2022.