The eastern Ukrainian city of Bakhmut was facing heavy artillery fire as the NATO chief backed reports from local officials that a major new Russian offensive had begun, days before the first anniversary of Moscow's invasion.
Ukrainian defenders, who have already held out for months, were braced for new ground attacks, Ukrainian military officials said on Monday.
Positions in Bakhmut have been fortified and only people with a military role were being allowed in, while any civilians who still wanted to leave the city would have to brave the incoming fire, a deputy battalion commander said on Monday.
Bakhmut is a prime objective for Russian President Vladimir Putin, and its capture would give Russia a new foothold in the Donetsk region and a rare victory after months of setbacks.
The Donetsk and Luhansk regions make up the Donbas, Ukraine's industrial heartland, now partially occupied by Russia which wants full control.
"We see how they are sending more troops, more weapons, more capabilities," NATO Secretary-General Jens Stoltenberg told reporters in Brussels, saying it was the start of a new offensive.
The Russian assault on Bakhmut has been spearheaded by mercenaries of the Wagner group, who have made small but steady gains. The renewed Russian bombardments made the situation there even more acute.
"The city, the city's suburbs, the entire perimeter, and essentially the entire Bakhmut direction and Kostyantynivka are under crazy, chaotic shelling," Volodymyr Nazarenko, deputy commander of Ukraine's Svoboda battalion, said on Monday.
"Thank you to every one of our soldiers who are preventing the occupiers from encircling Bakhmut... and who are holding our key positions at the front," President Volodymyr Zelenskiy said in his evening address.
The Russian defence ministry said its troops had pushed forward a few kilometres along the frontlines, without specifying where.
The Ukrainian military reported Russian shelling all along the frontline and said 16 settlements had been bombarded near Bakhmut. It said that over the past day, its forces had repelled attacks near Bakhmut as well as assaults in the Kharkiv, Luhansk and Zaporizhzhia regions.
The Ukrainian Governors of Luhansk and Donetsk have recently said that a predicted Russian offensive had begun. Luhansk governor Serhiy Haidai said Russian forces had attacked Bilogorivka from all sides before dawn on Monday.
Reuters was not able to independently verify the battlefield reports.
NATO to discuss further aid
The United Nations' human rights office said on Monday that it had recorded 7,199 civilian deaths and 11,756 wounded since Russia's Feb. 24 invasion, mostly from shelling and missile and air strikes. However, it believed the actual figure was far higher.
Russia invaded Ukraine on Feb. 24, 2022, in what it calls a "special military operation" to "denazify" the country and protect Russian speakers. Western leaders say it was nothing more than a land grab.
Moldova's President accused Russia on Monday of planning to use foreign saboteurs to bring down her leadership and use it in the war against Ukraine.
Zelenskiy said last week his country had uncovered a Russian intelligence plan "for the destruction of Moldova." Days later the government of the country, bordering Ukraine and Romania, resigned.
Russia denied last year wanting to intervene in Moldova after authorities in Transdniestria, a breakaway region that has survived for three decades with support from Moscow, said they had been targeted by a series of attacks.
White House national security spokesperson John Kirby on Monday said reports of the plot had not been independently confirmed but were "deeply concerning" and "certainly not outside the bounds of Russian behaviour."
With Ukraine desperate for more weapons, defence ministers from several NATO countries allied to Kyiv will meet in Germany on Tuesday to discuss possible further military aid.
On the eve of the meeting, Ukraine's top general and the most senior U.S. Army commander in Europe discussed military aid and training in a telephone conversation. Ukraine says it needs fighter jets and long-range missiles.
Stoltenberg said he expected the issue of aircraft to be discussed, but that Ukraine needed support on the ground now.
A NATO source said it would increase targets for the stockpiling of ammunition as Kyiv was burning through shells much faster than Western countries can produce.
"The current rate of Ukraine's ammunition expenditure is many times higher than our current rate of production," Stoltenberg told reporters.
Even before Russia's invasion of Ukraine, many NATO countries fell short of meeting the alliance's munitions stockpiling targets, as officials considered wars of attrition with large-scale artillery a thing of the past.
But the pace of deliveries to Ukraine, where Kyiv's troops are firing up to 10,000 artillery shells daily, has drained Western inventories.