Russian forces destroyed a theatre in Mariupol where hundreds of people were sheltering Wednesday and rained fire on other cities, Ukrainian authorities said, even as the two sides projected optimism over efforts to negotiate an end to the fighting.

The airstrike ripped apart the centre of the once-elegant building, where hundreds of civilians had been living since their homes had been destroyed in the fighting, Ukraine’s foreign ministry said in a statement.

Many people were buried in the rubble, the statement said, though there was no immediate word on how many had been killed or injured. Satellite imagery from Monday showed the word “children” written in large white letters in Russian in front of and behind the building, the Maxar space technology company said.

“My heart breaks from what Russia is doing to our people,” Ukrainian President Volodymyr Zelenskyy said in his nightly address, calling for more sanctions on Russia after the bombing.

The Russian defence ministry denied bombing the theatre or anywhere else in Mariupol on Wednesday.

In Kyiv, residents huddled in homes and shelters amid a citywide curfew that runs until Thursday morning, as Russian troops shelled areas in and around the city, including a residential neighbourhood 2.5 kilometres (1.5 miles) from the presidential palace. A 12-story apartment building in central Kyiv erupted in flames after being hit by shrapnel.

And 10 people were killed while standing in line for bread in the northern city of Chernihiv, the Ukrainian General Prosecutor’s Office said.

Earlier Wednesday, Zelenskyy went before the U.S. Congress via video and, invoking Pearl Harbor and 9/11, pleaded with America for more weapons and tougher sanctions against Russia, saying: “ We need you right now.”

U.S. President Joe Biden announced the U.S. is sending an additional $800 million in military aid to Ukraine, including more anti-aircraft and anti-tank weapons and drones. He also called Vladimir Putin a “war criminal” in his sharpest condemnation of the Russian leader since the invasion began.

International pressure against the Kremlin mounted and its isolation deepened as the International Court of Justice, also known as the World Court, ordered Russia to stop attacking Ukraine, though there was little hope it would comply. Also, the 47-nation Council of Europe, the continent’s foremost human rights body, expelled Russia.