Russia may be losing the “limited momentum” it had in the ruined town of Bakhmut, according to British military intelligence.
Fighting has raged for months in the small eastern city, the main target of Russia’s winter offensive, where some of the war's bloodiest battles have been fought.
Moscow succeeded in capturing the eastern part of the city and the outskirts to the north and south, but has so far failed to close a ring around Ukrainian defenders.
And now the UK's Ministry of Defence is seeing signs that Moscow’s forces are running out of steam.
“Over recent days Ukrainian forces initiated a local counterattack to the west of the Donetsk Oblast town of Bakhmut, which is likely to relieve pressure on the threatened H-32 supply route.
“Fighting continues around the town centre and the Ukrainian defence remains at risk from envelopment from the north and south.
“However, there is a realistic possibility that the Russian assault on the town is losing the limited momentum it had obtained, partially because some Russian MoD units have been reallocated to other sectors.”
Ukraine recently decided against pulling its forces out of the ruined city because the battle is pinning down Russia’s best units.
Mykhailo Podolyak, an aide to President Volodymyr Zelenskyy, said the fight for the beleaguered town was degrading Moscow’s elite troops before a planned Ukrainian spring counter-offensive.
Ukrainian forces said on Tuesday they had repelled Russian attempts to advance into the centre of Bakhmut.
In Russia, China's President Xi Jinping left Moscow on Wednesday, having given no direct support for Mr Putin's war in Ukraine during his two-day visit.
Mr Xi made a strong show of solidarity with Mr Putin against the West, but he barely mentioned the Ukraine conflict and said on Tuesday that China had an “impartial position.” There was no sign that Mr Xi's efforts to play the role of peacemaker had yielded results.
Yet, as Mr Xi departed he told Mr Putin: “Now there are changes that haven't happened in 100 years. When we are together, we drive these changes.”
“I agree,” Mr Putin said, to which Mr Xi responded: “Take care of yourself dear friend, please.”
Commenting on the meeting, the White House said China's position was not impartial and urged Beijing to pressure Russia to withdraw from Ukraine's sovereign territory, to end Europe's biggest conflict since the Second World War.
Ukraine and Russia conflict latest — in pictures
Overnight, while Mr Xi was in Moscow, Russian forces launched a “massive air strike,” firing 21 Shahed-136 drones, the General Staff of Ukraine’s Armed Forces said on Wednesday.
As Mr Xi prepared to leave Moscow, air-raid sirens blared across the capital Kyiv and in Ukraine's north and east, with reports of drone attacks, but no major destruction.
Mr Xi and Mr Putin referred to each other as dear friends, promised economic co-operation and described their countries' relations as the best they have ever been.
A statement released by China said: “They [the leaders] shared the view that this relationship has gone far beyond the bilateral scope and acquired critical importance for the global landscape and the future of humanity.”
Mr Putin said on the Kremlin's website: “We are working in solidarity on the formation of a more just and democratic multipolar world order, which should be based on the central role of the UN, its Security Council, international law, the purposes and principles of the UN Charter.”
In an earlier joint statement, the leaders accused the West of undermining global stability and Nato of barging into the Asia-Pacific region, but asserted the close partnership between China and Russia did not constitute a “military-political alliance.”
On Ukraine, Mr Putin praised Mr Xi for a peace plan he proposed last month, and blamed Kyiv and the West for rejecting it. The West sees China's peace plan as a ploy to buy Mr Putin time to regroup his forces and solidify his grip on occupied land.
China's 12-point plan has no specific details on how to end the bloody year-long war, which has claimed tens of thousands of lives and forced millions to flee.
The West has sought to isolate Russia through global sanctions and Mr Putin faces an arrest warrant from the International Criminal Court.
China has not supported any of the moves and the West is concerned it may help arm Russia in its conflict, which Beijing has denied.