Russia said on Monday its forces had made important gains in eastern Ukraine while continuing to fend off a new Ukrainian offensive inside the Kursk region of western Russia, where a second day of fierce fighting was under way.

It comes as Ukraine's president says only the US can provide security guarantees leading to an end to the war.

Russian forces continue to make costly but consistent gains in the Donetsk region in eastern Ukraine. They are steadily grinding down a pocket of resistance around the town of Kurakhove and are also fighting to envelop the larger nearby city of Pokrovsk, Ukrainian soldiers and officials said.