Over 100,000 civilians are stranded in the besieged city of Mariupol in southern Ukraine, Ukraine's Deputy Prime Minister Iryna Vereshchuk said Tuesday.

Civilians want to escape but could not because of the lack of safe humanitarian corridors out of the port city, Vereshchuk told a local television station.

The deputy PM also said residents had to walk for miles to reach the southeastern city of Zaporizhzhia.

She said shelling by Russian forces was also preventing rescue workers from accessing the site of a bombed theatre in Mariupol where authorities say hundreds were believed to be seeking shelter when it was hit by an airstrike last week.

More than 1,000 people, including women and children, were hiding in the building during the attack Wednesday, the Mariupol City Council said on Telegram.

The Russia-Ukraine war, which began on Feb. 24, has met international outrage with the EU, the United States and the United Kingdom, among others, implementing tough financial sanctions on Moscow.

At least 925 civilians have been killed during the war and nearly 1,500 injured, according to the United Nations tally.

The international body warns, however, that the true toll is "considerably higher."

More than 3.5 million people have fled Ukraine amid Russian attacks, according to the U.N. refugee agency.