One month into Russia's invasion of Ukraine, fire rained down on a shopping mall and high-rise buildings in Kyiv, as the outnumbered Ukrainian military waged intense battles to defend the capital and other key cities from falling under Russian control.

A barrage of strikes on cities have wreaked destruction across Ukraine over the past four weeks, but Russian forces appeared stalled outside major cities in the face of fiercer-than-expected Ukrainian resistance. NATO estimated on Wednesday that 7,000 to 15,000 Russian soldiers have been killed since the war started Feb. 24.

As U.S. President Joe Biden and key allies say they will meet this week to discuss possible new sanctions against Russia and more military aid for Ukraine, some of the millions who have fled are recounting scenes of horror. As one woman put it: "People are being killed day and night."

Here are some key things to know about the conflict:

WHAT IS HAPPENING ON THE GROUND?

The capital of Kyiv is still under fire. A barrage of shelling rocked the city on Wednesday, with rockets slamming into a shopping mall and high-rise buildings in the districts of Sviatoshynskyi and Shevchenkivskyi.

Destruction was extensive and fires from the shelling injured four residents, city officials said.

From a public park in Kyiv, mayor Vitali Klitschko said Russian bombardment had so far killed 264 civilians in the capital, including four children. As he spoke to reporters, explosions and loud gunfire echoed across the city.

Russian forces were also bombing the ancient city of Chernihiv in northern Ukraine, the governor said Wednesday, destroying a bridge that had been critical for evacuations and aid deliveries. Chernihiv residents are without clean water and gas for cooking and heating, city officials said.

On the capital's western outskirts, Ukrainian troops were trying to strike back at stalled Russian forces. Ukrainian forces managed on Tuesday to retake the suburban city of Makariv, allowing them to claw back a key highway and block Russian troops from surrounding Kyiv from the northwest. Ukrainian forces also have wrested back areas to the northwest and the northeast of the city, the Kyiv mayor said.

WHAT IS HAPPENING IN MARIUPOL?

Mariupol, a strategic port city on the Sea of Azov, has become a vivid symbol of the war's savage destruction.

Some 100,000 of Mariupol's prewar population of 430,000 remain trapped in the city, Ukrainian President Volodymyr Zelenskyy said. They are subject to relentless Russian bombardment from the sea and skies, and they are struggling to survive without heat, food or clean water.

Zelenskyy accused the Russians of seizing a humanitarian convoy that was trying to get desperately needed food and supplies to residents. Deputy Prime Minister Iryna Vereshchuk said 11 bus drivers and four rescue workers were being held captive.

Zelenskyy said what's happening in Mariupol is "inhumane." United Nations Secretary-General Antonio Guterres described the situation as a "living hell."

WHAT HAS THE AP DIRECTLY WITNESSED OR CONFIRMED?

Firefighters sprayed water on a smoldering residential building that was demolished by Russian shelling in western Kyiv early Wednesday. Fire service spokesperson Svitlana Vologda spoke with The Associated Press as the sound of fighting rumbled in the distance.

"If we're talking about numbers of requests for firefighters to respond, it's the largest one since the start of the war," Vologda said.

Kyiv was shaken by a constant barrage of shelling Wednesday. Plumes of black smoke rose from the western outskirts of the city.

In the seaside city of Odesa, fondly known as the Pearl of the Black Sea, street musicians played under cloudless skies as people fled.

Odesa has so far been spared the worst of Russia's onslaughts, but a major attack on Ukraine's biggest port city seems inevitable. Anxiety is growing. The streets are stacked with sandbags and barricades. Tearful families waved goodbye to loved ones at the train station.

"I can't understand what has happened," said Igor Topsi, a musician.

WHAT ARE UKRAINIAN REFUGEES SAYING?

Some of the more than 3.5 million people who have fled Ukraine since the invasion began have shared nightmarish stories of death, destruction and the painful separation from loved ones.

Natalia Savchenko, 37, arrived in Medyka, Poland, on Wednesday and said the situation in the eastern city of Kharkiv is "terrible." She said there is no electricity or water, and children are not being given medicine or food.

"People are being killed day and night. They are shooting with everything they have," she said.

At the train station in Przemysl, Poland, Kateryna Mytkevich said her family was trapped at home in the northern city of Chernihiv for three weeks and hoped the war would pass them by — but then "bombs began to fall."

"Our children are dying. My son had to stay in Chernihiv, I could only take my daughter with me. It hurts a lot. Now we have nowhere to go, our whole neighborhood is destroyed. Everything is completely destroyed," said Mytkevich, 39.

Volodymr Fedorovych, 77, also fled Chernihiv, saying: "There was nothing, there wasn't even bread." He said bread was brought in every three days, and on one day, he walked away from the bread line to get some tea when a bomb fell without warning.

"Sixteen people died and 47 were taken by ambulance, some of them without arms and legs. Horrible. There were one hundred people in that queue," he said. Ukrainian officials have said that 10 people were killed in the bombing of a bread line last week.

HAVE RUSSIAN AND UKRAINIAN TROOPS TAKEN HEAVY LOSSES?

That's been hard to determine, as official numbers have not been regularly released by either country.

In its first public estimate of Russian casualties since the war began, NATO estimated Wednesday that 7,000 to 15,000 Russian soldiers have been killed. A senior NATO military official said that estimate was based on information from Ukrainian officials, what Russia has indicated and intelligence gathered from open sources. The official spoke on condition of anonymity under ground rules set by NATO.

Russia has released little information. Back on March 2, Russia said nearly 500 soldiers had been killed and almost 1,600 wounded.

The most recent figure for Ukraine's military losses came from Zelenskyy on March 12, when he said that about 1,300 Ukrainian servicemen had been killed in action.

Ukraine also claims to have killed six Russian generals. Russia acknowledges just one dead general.

— Associated Press writer Robert Burns in Washington contributed to this report.

HOW IS THE WORLD RESPONDING TO THE WAR?

President Biden headed to Brussels on Wednesday for talks with key allies, an effort to try to keep the war from becoming an even greater catastrophe.

As he departed Washington, he described the possibility that Russia could use chemical weapons in Ukraine as a "real threat." It's an issue world leaders will discuss at the NATO summit, he added.

Biden is expected to roll out new sanctions on Russia and coordinate more military assistance for Ukraine. He's also working on long-term efforts to boost defenses in Eastern Europe and wean the continent off Russian oil and gas, the White House said. He will travel to Poland later in the week.

From the Vatican, Pope Francis again prayed for peace in Ukraine. He added a personal note this time to explain his aversion to conflict, citing his grandfather, a World War I veteran, who taught him to hate war in all its forms.

International investigations of possible war crimes and other violations in the war are underway. The Swiss attorney general's office says it has started collecting evidence from Ukrainian refugees in an effort to expose potential crimes and breaches of sanctions.

In the latest stop of his global tour via video conference, Zelenskyy delivered an emotional speech to the Japanese parliament. He implored lawmakers to help Ukraine defend itself and impose more sanctions on Russia.

"Our people cannot even adequately bury their murdered relatives, friends and neighbors," he said.

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