Several explosions hit the city of Lviv, in western Ukraine, regional officials said.
The governor of the Lviv region, Maksym Kozytskyi, said five people had been injured, and that rocket fire had hit a fuel storage facility and a factory.
Lviv has so far escaped much of the shelling that has come to be a part of daily life in other parts of Ukraine.
It has also become a hub for hundreds of thousands of refugees fleeing other parts of the country.
The alleged Russian attack came as US President Joe Biden delivered a speech in Warsaw, Poland, some 250 miles (400km) from Lviv.
In it, he addressed the Russian people on their leader, President Vladimir Putin, telling them: “For God’s sake, this man cannot remain in power.”
The Kremlin responded that was not for the US leader to say. “That’s not for Biden to decide. The president of Russia is elected by Russians,” a spokesman said.
A White House official later said that Mr Biden was not calling for “regime change”, but making the point that Vladimir Putin cannot be allowed to exercise power over his neighbours in the region.
Lviv’s mayor, Andriy Sadoviy, said that “with today’s blows, the aggressor sends greetings to President Biden, who is in Poland,” Reuters news agency reports.
‘Nobody really cares’
By Hugo Bachega, BBC News, Lviv
First, mid-afternoon, the air raid sirens went off. Then, three powerful explosions, and thick plumes of smoke could be seen from the distance. Hours later, another attack.
It all happened a day after Russia said it was focusing its invasion of Ukraine on the east. Lviv is in the extreme opposite.
And this distance from the worst of Russia’s aggression, where people have been under unrelenting bombing and shelling, turned this city into something like a safe heaven. Displaced people, humanitarian workers, volunteers. They are all here.
That perception could be changing. Maryanna Pack, a 39-year-old economist who was near the site of the blast, gave a passionate testimony that may be a view shared by many. “We’re feeling unprotected. Nobody really cares about what’s happening here,” she said.
“We need more help now. Eastern Ukraine has been completely destroyed. It’s really possible that could happen to Lviv and the west of the country too.”
