Ukrainian President Volodymyr Zelenskyy invoked Pearl Harbor and 9/11 during a rare and urgent appeal Wednesday to the U.S. Congress for more weapons to stem the Russian assault, even as he projected optimism that Moscow's demands for halting the nearly three-week war were becoming "more realistic."

"We need you right now," Zelenskyy said in remarks livestreamed to the U.S. Capitol, which were punctuated with a graphic video contrasting Ukraine before the invasion with the grisly aftermath.

He spoke on a day a Russian airstrike destroyed a theater building where hundreds of people were sheltering in the encircled seaport of Mariupol, officials said. There was no immediate word on deaths or injuries. The Russian offensive also pressed closer to Ukraine's seat of government, as missiles and artillery slammed into high-rise apartment towers in Kyiv, setting buildings ablaze and sending smoke over the capital and its suburbs.

Russian President Vladimir Putin said Wednesday that the operation in Ukraine is unfolding "successfully, in strict accordance with pre-approved plans."

But both sides also signaled a glimmer of hope ahead of a fourth round talk of talks scheduled for Wednesday between Russian and Ukrainian negotiators.

With the Ukrainian resistance frustrating the Kremlin hopes for a lightning victory, Russian Foreign Minister Sergey Lavrov said that a "business-like spirit" has emerged in the diplomatic talks, which he described as focused on a "neutral status" for Ukraine's military. Zelenskyy urged patience as officials prepared to return to the negotiating table.

Here are some key things to know about the conflict:

WHAT IS HAPPENING ON THE GROUND?

Shrapnel from an artillery shell smashed into a 12-story apartment building in the center of Kyiv early Wednesday, wiping out the building's top floor and sparking a fire. Emergency services reported two victims from the blaze, without specifying if they were killed or injured.

The leaping flames and thick smoke that have engulfed Kyiv apartment towers in recent days pointed to a possible new stage in the war, puncturing the sense of calm that had returned to the capital after Russia's initial advance.

Fighting continued to rage in Kyiv's suburbs, depriving thousands of heat and clean water. Russian troops were seeking to sever the capital from transport routes and supply lines as they planned a wider assault, a local official said.

A Russian airstrike slammed into the town of Markhalivka southwest of the capital and destroyed multiple residential apartments, authorities added. The extent of the damage remained unclear.

Russia now occupies the city of Ivankiv, 80 kilometers (50 miles) north of Kyiv, and controls the surrounding region on the border with Belarus, local officials said.

Relentless strikes pounded the northeastern city of Kharkiv close to the Russian border that has suffered repeated bombardment. Ukrainian forces continued to thwart Russia's incursion into the heart of the city, city officials said.

Powerful explosions also thundered in the region around Kherson, a strategic Black Sea port, and near a train station in the southeastern energy-production hub of Zaporizhzhia.

The region "is on the verge of a humanitarian catastrophe," Zelenskyy's office warned.

ARE UKRAINIANS ABLE TO EVACUATE?

In the southeast, over 28,800 civilians escaped the blockaded port of Mariupol through several humanitarian corridors.

The successful evacuation came even as Russian forces have renewed their shelling on the coastal city, where hundreds of thousands of civilians have struggled to stay alive without heat, food and clean water. Russian troops seized the city's largest hospital late Tuesday, holding hundreds people hostage inside the building, a regional official said.

Humanitarian convoys again failed to make it into Mariupol because of the Russian assault but managed to deliver aid and set up evacuation corridors from Ukraine's northeastern Sumy region. The head of the Red Cross, which has helped organize the evacuations, arrived in Kyiv Wednesday to push for better humanitarian aid access and protection for civilians.

Overall, more than 3 million refugees have fled Ukraine, the U.N. said — Europe's largest refugee crisis since WWII.

WHAT HAS THE AP DIRECTLY WITNESSED OR CONFIRMED?

In Mariupol, workers afraid for their own lives brave relentless shelling to dump the bodies of children in a mass grave. Local officials struggle to account for the dead. Although they've tallied 2,500 deaths in the siege, many bodies crushed in the rubble can't be counted because of the assault.

Bodies lie out in the street. Workers tell families to leave their dead outside because it's too dangerous to hold funerals.

"Why? Why? Why?" sobbed Marina Yatsko from a hospital hallway, after medical workers could not save her toddler, struck in the head by shrapnel.

In the chaos and destruction of besieged Kharkiv, doctors are struggling to treat COVID-19 patients as the bombs fall outside.

Several times a day, air raid sirens wail at the Kharkiv Regional Clinical Infectious Diseases Hospital, sending feeble virus patients — some connected to ventilators and struggling to breathe — running for bomb shelters.

"Bombing takes place from morning into night," hospital director Dr. Pavel Nartov told The Associated Press. "It could hit at any time."

HOW IS THE WORLD RESPONDING TO THE WAR?

Zelenskyy acknowledged in his speech to the U.S. Congress that the no-fly zone he has sought to "close the sky" over his country may not happen. Still, he said the U.S. must sanction Russian lawmakers and block imports, in addition to providing military assistance.

"I see no sense in life if it cannot stop the deaths," he told them in English after giving most of his speech in Ukrainian through an interpreter.

In an unprecedented move, the Council of Europe expelled Russia from the continent's foremost human rights body. Staff even went outside the Council's headquarters in Strasbourg, France, and took down the Russian flag.

Tiny Kox, the President of the Parliamentary Assembly of the Council of Europe, said the expulsion "was necessary, and I am glad we dared to do so."

The leaders of three European countries, Poland, the Czech Republic and Slovenia, returned on Wednesday from a risky trip to the besieged Ukrainian capital to show their support and meeet with Zelenskyy as fires burned in the wreckage outside.

U.S. President Joe Biden announced that the country is sending an additional $800 million in military assistance — including anti-aircraft and anti-armor weapons and drones — to Ukraine, making a total of $2 billion in such aid sent to Kyiv since Biden took office more than a year ago.

Biden also plans to travel to Europe next week for face-to-face talks with European leaders about the Russian invasion, and will attend an extraordinary NATO summit in Brussels. NATO has been bolstering its eastern flank with troops and equipment to deter Russia from invading any of its members.

Around the word, governments continued to punish Moscow for its war. The U.S. targeted the assets of Russian military officials in an additional round of sanctions. The European Union imposed sanctions on Chelsea FC owner Roman Abramovich and announced new measures to deny Russian oligarchs high-end luxury goods.

Japan announced it will revoke its "most favored nation" trade status for Russia over its invasion of Ukraine.

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