Invading Russian forces have bombed a theater where civilians were sheltering in the encircled port city of Mariupol, the city council said Wednesday.

It said the number of casualties was not yet known.

Reuters could not independently verify the information.

Russia denies targeting civilians.

Russian troops put a blockade on the strategic Ukrainian port city Mariupol, the mayor announced Saturday.

Capturing Mariupol, a city of about 450,000 people on the Azov Sea, would represent a bigger prize for Russian forces as it would deal a severe blow to Ukraine's maritime access and connect troops coming from annexed Crimea and the Donbass region.

Since Russia launched its war on Ukraine on Feb. 24, more than 2.5 million people have fled to other countries, with some 2 million more displaced within the country.

At least 564 civilians have also been killed and 982 others injured in Ukraine, according to U.N. estimates.

While the European Union, United States and others have imposed sanctions on Moscow, many companies and global brands have also suspended operations in Russia.