The United States on Tuesday urged its citizens to leave Ukraine, saying it believed Russia was preparing to target civilian and government infrastructure in the next few days as the war reaches the six-month mark.
The warning followed a ban by the Ukrainian government on celebrations in the capital Kyiv on Wednesday's anniversary of independence from Soviet rule due to fears of attack.
On the battlefield, Russian forces carried out artillery and air strikes in the Zaporizhzhia region in southeastern Ukraine, where fighting has taken place near Europe's largest nuclear power plant, the Ukrainian military said.
But six months on from Russia's February 24 invasion of Ukraine, and with thousands of deaths and widespread destruction of cities, the conflict is locked in a stalemate.
Russian forces control a large swathe of the south, including along the Black Sea coast, and chunks of the eastern Donbas region. The prospects for peace look almost non-existent.
Fearing a surge in Russian attacks, the US Embassy in Kyiv on Tuesday urged US citizens to leave if they could.
"The Department of State has information that Russia is stepping up efforts to launch strikes against Ukraine’s civilian infrastructure and government facilities in the coming days," the embassy said in a statement.
US citizens should leave Ukraine "now" by their own means if it was safe to do so, it said.
Although it was not the first time the United States has issued such a warning, this one was made as Ukraine was due on Wednesday to mark 31 years of independence from Soviet rule.
It also followed the killing of Darya Dugina, the daughter of a prominent Russian ultra-nationalist, in a car bomb attack near Moscow on Saturday. Moscow has blamed the killing on Ukrainian agents, an accusation Kyiv denies.
Ukrainian President Volodymyr Zelenskiy has also said Moscow could try "something particularly ugly" in the run-up to Wednesday's anniversary.
Kyiv is far from the frontlines and has only rarely been hit by Russian missiles since Ukraine repelled a ground offensive to seize the capital in March.
Meanwhile Polish President Andrzej Duda, one of Ukraine's strongest supporters, arrived in the capital on Tuesday to discuss further support for Ukraine, including military aid. He was due to meet Zelenskiy.