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.
In other developments in Ukraine today:
- The city of Slavutych, where many of Chernobyl’s nuclear power plant’s workers live, was taken by Russian troops, according to the regional governor. Local residents waved Ukrainian flags and sang patriotic songs in protest.
- Russian forces fired at a nuclear research facility in the north-eastern city of Kharkiv, according to Ukraine’s parliament. It said it was unable to assess the extent of the damage to the site because of the continued Russian shelling of the city.
- Another Russian general, Lt Gen Yakov Rezantsev, was killed in a strike near the southern city of Kherson, said Ukraine’s defence ministry.
‘Nobody really cares’
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.”
As bombs fell on Lviv and other cities across Ukraine, President Biden referred to his Russian counterpart as “a butcher”.
The comment was made during a meeting with Ukrainian refugees helping with the humanitarian relief effort in Poland – where more than two million Ukrainian refugees have now fled.
A spokesperson for Mr Putin, cited by Russian state news agency Tass, said the comment narrowed the prospects for mending ties between the two countries.
Earlier, Mr Biden met Ukraine’s foreign and defence ministers, Dmytro Kuleba and Oleksii Reznikov.
The two Ukrainian’s ministers’ trip out of Ukraine to Poland was seen as a possible sign that confidence in Ukraine’s fightback against Russia is growing.
During the talks, the US’s “unwavering commitment to Ukraine’s sovereignty and territorial integrity” was discussed, according to a US state department spokesperson.
Mr Biden also stressed the “sacred commitment” to Nato’s collective defence, after meeting with Polish President Andrzej Duda.
“You can count on that… for your freedom and ours,” he told Mr Duda.