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

There was no immediate word on deaths or injuries in what the Mariupol city council said was an airstrike on the theater.

In Kyiv, residents huddled in homes and shelters amid a citywide curfew that runs until Thursday morning, as Russia shelled areas in and around the city, including a residential neighborhood 2.5 kilometers (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.

Ukrainian President Volodymyr Zelenskyy, meanwhile, 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 later announced the United States is sending an additional $800 million in military aid to Ukraine, including more anti-aircraft and anti-tank weapons and drones.

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.

While Moscow's ground advance on the Ukrainian capital appeared largely stalled, Russian President Vladimir Putin said the operation was unfolding "successfully, in strict accordance with pre-approved plans," and he decried Western sanctions against Moscow. He accused the West of trying to "squeeze us, to put pressure on us, to turn us into a weak, dependent country."

Another round of talks between the two sides was scheduled for Wednesday. After Tuesday's negotiations, Russian Foreign Minister Sergey Lavrov said a neutral military status for Ukraine was being "seriously discussed" by the two sides, while Zelenskyy said Russia's demands for ending the war were becoming "more realistic."

Hopes for diplomatic progress to end the war rose after Zelenskyy acknowledged Tuesday in the most explicit terms yet that Ukraine is unlikely to realize its goal of joining NATO. Putin has long depicted Ukraine's NATO aspirations as a threat to Russia.

Lavrov welcomed Zelenskyy's comment and said "the businesslike spirit" starting to surface in the talks "gives hope that we can agree on this issue."

"A neutral status is being seriously discussed in connection with security guarantees," Lavrov said on Russian TV. "There are concrete formulations that in my view are close to being agreed."

Russia's chief negotiator, Vladimir Medinsky, said the sides were discussing a possible compromise for a Ukraine with a smaller, non-aligned military.

Prospects for a diplomatic breakthrough were highly uncertain, however, given the gulf between Ukraine's demand that the invading forces withdraw completely and Russia's suspected aim of replacing Kyiv's Westward-looking government with a pro-Moscow regime.

Ukrainian presidential adviser Mykhailo Podolyak denied Russian claims Ukraine was open to adopting a model of neutrality comparable to Sweden or Austria. Podolyak said Ukraine needs powerful allies and "clearly defined security guarantees" to keep it safe.

Another source of dispute is the status of Crimea, which was seized and annexed by Russia in 2014, and the separatist-held Donbas region in eastern Ukraine, which Russia recognizes as independent. Ukraine considers both part of its territory.

The fighting has sent more than 3 million people fleeing Ukraine, by the United Nations' estimate. The U.N. reported that over 700 civilians have been confirmed killed but that the real number is higher.

In going before Congress, Zelenskyy said that Russia "has turned the Ukrainian sky into a source of death for thousands of people." But Biden has resisted Zelenskyy's requests to send warplanes to Ukraine or establish a no-fly zone over the country because of the danger of triggering war between the U.S. and Russia.

The head of the International Committee of the Red Cross, Peter Maurer, arrived in Ukraine to try to obtain greater access for aid groups and increased protection of civilians.

Amid the vast humanitarian crisis caused by the war, the Red Cross has helped evacuate civilians from besieged areas and has delivered 200 tons of aid, including medical supplies, blankets, water and over 5,200 body bags to help "ensure the dead are treated in a dignified manner."

Nowhere has suffered more than the encircled city of Mariupol, where local officials say missile strikes and shelling have killed more than 2,300 people. The southern seaport of 430,000 has been under attack for almost all of the three-week war in a siege that has left people struggling for food, water, heat and medicine.

Local authorities said Russian forces took hundreds of people hostage at a Mariupol hospital and were using them as human shields.

Bodies have been buried in trenches in Mariupol, and more corpses lay in the streets and in a hospital basement.

Using the flashlight on his cellphone to illuminate the basement, Dr. Valeriy Drengar pulled back a blanket to show the body of an infant 22 days old. Other wrapped bodies also appeared to be children, given their size.

"These are the people we could not save," Drengar said.

Nearly 30,000 people managed to escape the city on Tuesday in thousands of vehicles by way of a humanitarian corridor, city officials said.

But with humanitarian aid unable to get in amid the constant bombardment, people burn scraps of furniture to warm their hands and cook the little food still available.

Kyiv regional leader Oleksiy Kuleba said Russian forces had intensified fighting in the Kyiv suburbs and a highway leading west, and across the capital region, "kindergartens, museums, churches, residential blocks and engineering infrastructure are suffering from the endless firing."

In other developments, the mayor of the city of Melitopol, who was seized by Russian forces five days ago, has been freed, said Zelenskyy chief of staff Andriy Yermak. No details were given about how he became free.

Ukraine also appeared to have successes, with satellite photos from Planet Labs PBC analyzed by The Associated Press showing helicopters and vehicles ablaze at the Russian-held Kherson airport and air base after a suspected Ukrainian strike on Tuesday.

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Associated Press journalists around the world contributed to this report.

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Follow AP's coverage of the war at https://apnews.com/hub/russia-ukraine