Russian forces were trying to close their circle around the small mining city of Bakhmut on Monday, while rain and an early spring thaw turned east Ukraine's battlefields to mud which could hamper both sides as they try to take the initiative.
The spring thaw, known as the rasputitsa, has a long history of ruining plans by armies to attack across the soil of Ukraine and western Russia, turning roads into rivers and fields into impenetrable bogs.
In the Donetsk region near the front, Ukrainian soldiers hunkered in muddy trenches after suddenly warmer weather softened the frozen ground.
"Both sides stay in their positions, because as you see, spring means mud. Thus, it is impossible to move forward," said Mykola, 59, commander of a Ukrainian frontline rocket launcher battery, watching a tablet screen for coordinates to fire.
Reuters saw several military vehicles stuck in mud. In a trench, cut deeply out of the ground in a zigzag pattern, Volodymyr, a 25-year-old platoon commander, said his men were prepared to operate in any weather.
"When we're given a target that means we have to destroy it."
Russia is trying to encircle Bakhmut, forcing Ukraine to pull out its garrison. That would give Moscow its first major prize in more than half a year, following one of the bloodiest phases of the war so far - a relentless Russian assault that began over frozen ground.
Its forces replenished with hundreds of thousands of reservists called up late last year, Russia has intensified its attacks on several locations along the front in the east. Western countries say several of Russia's assaults have failed at high cost.
But Moscow's troops have made clear, if slow, progress north and south of Bakhmut, attempting to cut off Ukrainian forces inside the ruined city, which once held around 75,000 people.
"Vicious battles are going on there. The command is doing everything it can to stop the enemy from advancing through our territory," Serhiy Cherevatyi, a spokesperson for Ukraine's eastern military command, told Ukrainian television, describing the situation around Bakhmut.
For it's part, Moscow claimed to have destroyed a Ukrainian ammunition depot near Bakhmut and shot down US-made rockets and Ukrainian drones. Reuters could not verify the battlefield reports.
YELLEN IN KYIV
In Kyiv, US Treasury Secretary Janet Yellen became the latest senior Western official to visit the Ukrainian capital, promising assistance and more measures to isolate Russia. Her boss, President Joe Biden, went there are a week ago to mark the first anniversary of the war.
"America will stand with Ukraine as long as it takes," Yellen, flanked by sandbags at the cabinet ministers' office, told Ukrainian Prime Minister Denys Shmyhal.
Yellen announced the transfer of the first $1.25 billion from the latest, $9.9 billion tranche of economic and budget assistance from Washington, and visited a school where teacher salaries are reimbursed by US budgetary support.
Ukraine's military forces have mostly focused on holding defensive positions in recent weeks, but are expected to attempt a counter-offensive later this year using new weapons pledged by the West.
"I really want (victory) to happen this year. For this we have everything – motivation, confidence, friends, diplomacy," Zelensky said in a post on the Telegram messaging app on Monday.
The anniversary of the war last week saw efforts from both sides to demonstrate their resolve for a second year of fighting.
Russian President Vladimir Putin, who launched the invasion a year ago, gave a major speech in which he abandoned the last remaining nuclear arms control treaty with the United States but announced no major initiatives to change course in the war.
He was upstaged by Biden, who journeyed to Kyiv and gave a landmark speech of his own in Warsaw.
China, which signalled support for Russia by sending its top diplomat to Moscow last week, has issued a call for peace.
The step has been met sceptically by the West but welcomed in general terms by both Kyiv and Moscow. Washington has said in recent days it worries that China could send weapons to Russia, which Beijing denies.
Russia says the invasion was justified by a security threat posed by Ukraine. Kyiv calls it an unprovoked attempt to subjugate an independent state.
Ukraine's outnumbered troops repelled Russia's attack last year on the capital Kyiv and recaptured substantial territory, but Moscow continues to occupy nearly a fifth of Ukraine which it claims to have annexed.
Tens of thousands of Ukrainian civilians and soldiers on both sides are believed to have been killed.