Battles are raging in a key stronghold of Ukrainian forces in the eastern region of Donetsk, one year after Russia began its invasion.

The founder of Russian private military company Wagner Group said on Saturday it had captured the village of Yahidne, about 2 kilometers north of the city of Bakhmut.

He said the previous day that his group had seized Berkhivka, another village near the city.

Ukraine said its military commander had entered Bakhmut and encouraged Ukrainian soldiers.

A US think tank, the Institute for the Study of War, said on Saturday that Russian forces had "made marginal territorial gains" around areas that included Bakhmut.

On Sunday, Russia's state-run news agency reported a state TV interview with President Vladimir Putin.

Putin said the outcome of the past year was the unity of the Russian people. He stressed that Russia will not lose as long as it continues to unite.

Putin also said he must take into account NATO's nuclear capabilities, and future nuclear arms control negotiations should also cover British and French nuclear weapons.