Ukrainian President Volodymyr Zelenskyy says Russian forces have suffered more than 38,000 casualties in the western Russian region of Kursk over the five months since Kyiv launched its cross-border offensive there.

In a speech on Monday, marking five months into the Kursk operation, Zelenskyy said that about 15,000 of those soldiers had died.

In Kursk, intense fighting continues as Ukrainian forces launched a new offensive in the region on Sunday. Russian forces, together with North Korean soldiers, aim to regain lost territory.

Kyiv apparently wants to take control of as much territory as possible ahead of the inauguration of US President-elect Donald Trump on January 20, as a bargaining chip for possible peace talks. Russia likely aims to block such moves.

Meanwhile, Russian President Vladimir Putin attended a church service for the Russian Orthodox Christmas holiday, which starts on Tuesday. He was joined by veterans of the Ukraine conflict at the church in Moscow's Victory Park.

Putin said in a statement that "the Russian Orthodox Church and other Christian denominations in Russia play a tremendous creative role in uniting the people and in preserving our historical memory and unique cultural and spiritual heritage."