Russian forces remain relentless in their attempts to take full control of the bombed-out eastern Ukrainian towns of Bakhmut and Avdiivka but were not making progress, Ukrainian military officials said, as a Russian-installed official claimed otherwise.

The two towns along with nearby communities in the industrial Donetsk region continued to receive the brunt of Russia's attacks, the General Staff of the Ukrainian Armed Forces said in its Tuesday evening statement.

"They simply try to exhaust our troops with attack after attack," Serhiy Cherevatiy, spokesman for the eastern group of Ukrainian troops, said on national television on Tuesday night, reporting 70 shelling incidents in Bakhmut alone.

But the military said Ukrainian fighters continued to successfully repel Russian forces and claimed that Russia was suffering high combat deaths in the offensive.

Reuters was not able to verify any of the battlefield accounts.

Away from the battlefields of the biggest land conflict in Europe since World War Two, Russian ally Belarus confirmed it will host Russian tactical nuclear weapons, saying the decision was a response to Western sanctions and what it said was a military build-up by NATO member states near its borders.

US President Joe Biden indicated he would be concerned by the move. But the United States said on Tuesday that it had not seen any indications that Russia was closer to using tactical nuclear weapons in Ukraine.

Rafael Grossi, head of the United Nations nuclear watchdog, said in an interview that his work on forging an agreement to protect the Russian-occupied Zaporizhzhia nuclear power plant in southern Ukraine was still alive. On the eve of his expected visit to the plant on Wednesday, he described the situation there as very dangerous and very unstable.

Ukrainian President Volodymyr Zelenskiy visited two northern towns and trenches near the Russian border on Tuesday. In his nightly video address, Zelenskiy mentioned the international response to Russia's February 2022 invasion of his country, saying it "reminds the world that Russian aggression could be ended considerably more quickly than is sometimes said."

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Russian tanks hit, UK says

What Moscow has called a "special military operation" in its pro-Western neighbour to reduce a threat to its own security has killed thousands of troops on both sides, tens of thousands of Ukrainian civilians and displaced millions. The invasion also shook the global economy and disrupted international relations.

One dispute is over whether Russian and Belarusian athletes can return to international competitions. On Tuesday, the International Olympic Committee issued recommendations for their gradual return as neutrals.

IOC President Thomas Bach said their participation "works" despite the war in Ukraine. But countries opposed to the idea rejected them and Russia's Olympic chief called them "absolutely unacceptable".

Britain's defence ministry said Russian forces had made only "marginal progress" in an attempt to encircle Avdiivka in recent days and had lost many armoured vehicles and tanks. The UK, the United States and European allies of Ukraine have provided the Kyiv government with weapons and money, describing the invasion as an imperial-style land grab by Russia.

Denis Pushilin, the Russian-installed leader of the part of Donetsk region under Moscow's control, said most Ukrainian forces had pulled back from a metals factory in western Bakhmut. Pushilin's claims ran counter to Ukrainian and Western assertions that the situation in Bakhmut is stabilising and that Russia's winter offensive is faltering.

Ukrainian military commanders have said their own counteroffensive - backed by newly delivered Western hardware, including German Leopard 2 tanks - is not far off, but have stressed the importance of holding Bakhmut in the meantime.

"In principle, we cannot speak of them (Russian forces) having achieved any strategic advances in the last few hours or even days," Ukrainian spokesman Cherevatiy said. "We fire on them to inflict maximum casualties on troops and materiel, break their offensive thrust and keep them from securing any advantage."

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