Russian forces are pounding Ukrainian cities and edging closer to the capital, Kyiv, in a relentless bombardment that keeps deepening the humanitarian crisis in this war, now in its third week.

Still, a narrow diplomatic channel remains open, with a Ukrainian official saying Tuesday’s talks with the Russians were difficult, but that there was room for compromise.

Ukrainian President Volodymyr Zelenskyy told European leaders gathered in London on Tuesday that he realizes NATO has no intention of accepting Ukraine. Zelenskyy has this indicated before but this statement was more explicit. Russia has demanded that Ukraine drop its bid to join NATO, adopt a neutral status and demilitarize.

U.S. President Joe Biden will announce Wednesday the U.S. is delivering more military assistance to Ukraine, including anti-armor and air defense weapons. Zelenskyy is scheduled to speak to Congress Wednesday via video.

Here are some key things to know about the conflict:

WHAT IS HAPPENING IN AND AROUND KYIV?

Artillery fire echoed through Kyiv on Tuesday as Russia launched strikes that ignited a huge fire in a 15-story apartment building apartment. Zelenskyy said barrages also hit four multi-story buildings, killing dozens of people.

Explosions caused significant structural damage, with shockwaves from a blast tearing through the entrance of a downtown subway station that residents have used as a bomb shelter.

SHOWING SUPPORT FOR UKRAINE

The leaders of Poland, the Czech Republic and Slovenia traveled to Kyiv by train Tuesday in a show of support for Ukraine. Janez Jansa of Slovenia described the visit as sending the message that Ukraine is a European country that deserves to be accepted into the European Union one day.

The leader of the Ukrainian Catholic Church in the United States appealed Tuesday for humanitarian aid as well as weapons to help Ukrainians fight Russia’s invasion. The Most Rev. Borys Gudziak asked what good does it do to feed the citizens of Ukraine “if their brains are going to be blown out, if their apartment buildings are going to be rendered into rubble?”

WHAT IS HAPPENING IN MARIUPOL, OTHER CITIES?

After days of relentless Russian shelling of Mariupol, an estimated 20,000 civilians used a humanitarian corridor to flee the port city. The route runs west for more than 260 kilometers (160 miles) to the Ukraine-held city of Zaporizhzhia.

Russian troops seized a hospital in Mariupol and took about 500 people hostage during another assault on the southern port city late Tuesday, regional leader Pavlo Kyrylenko said. The soldiers drove 400 people from neighboring homes into Regional Intensive Care Hospital and about 100 doctors and patients also are believed to be inside, he said.

Ukraine said a Russian general has been killed during the storming of Mariupol. Maj. Gen. Oleg Mityaev, who commanded the 150th motorized rifle division, died Tuesday, said Ukrainian Interior Ministry adviser Anton Gerashchenko. There was no confirmation from Russia on the fourth reported death of a Russian general in Ukraine.

In the east, Russian forces blasted downtown Kharkiv with artillery, hitting the city’s historical center, including its main marketplace. Rescuers were pulling the bodies of dead civilians from destroyed apartment buildings.

FOX NEWS JOURNALISTS KILLED

Two journalists working for Fox News were killed and one was injured when the vehicle they were traveling in was hit by incoming fire on Monday near Kyiv, the network said Tuesday.

Video journalist Pierre Zakrzewski, 55, died along with Ukrainian journalist Oleksandra “Sasha” Kuvshynova, 24, who was helping the Fox crews navigate the country. Another reporter, Benjamin Hall, was injured.

The London-based Zakrzewski had covered conflicts in Iraq, Afghanistan and Syria and played a key role last year in getting Fox’s freelancers and their families out of Afghanistan after the U.S. withdrawal, the network said.

The attack happened a day after documentary filmmaker Brent Renaud was killed when Russian forces opened fire on his vehicle.

WHAT HAS THE AP DIRECTLY WITNESSED OR CONFIRMED?

Flames gutted an apartment building in the Svyatoshynskyi district of western Kyiv as emergency workers climbed ladders to rescue people.

Thick, dark smoke choked the air. A firefighter at the scene confirmed one person had died and that several have been rescued alive — but more remained trapped inside. A young woman sobbed outside the charred building, where shocked residents assessed the damage.

“People are dying, and the worst thing is that children are dying,” said Andriy, a firefighter at the scene who would only give his first name, before heading back into the burning building.

Meanwhile, a small but growing number of people are heading back to Ukraine to help, from foreign volunteers to Ukrainian expatriate men and more recently women.

“I will go back and help. I am a health worker, so the hospitals need help,” said Iryna Orel, 50, lugging her luggage as she boarded a train from Przemysl, Poland, to Lviv in western Ukraine. “And I will stay until the end.”

WHAT IS THE STATUS OF DIPLOMACY IN THE RUSSIA-UKRAINE WAR?

Zelenskyy said early Wednesday that Russia’s demands during negotiations are becoming “more realistic.”

After Ukrainian negotiators met with their Russian counterparts, Ukrainian presidential aide Ihor Zhovkva said Tuesday’s talks were more constructive. Talks are scheduled to continue Wednesday.

Russia has circulated a proposed U.N. Security Council resolution demanding protection for civilians “in vulnerable situations” in Ukraine along with safe passage for humanitarian aid and people seeking to leave the country, without mentioning Russia’s responsibility for the war.

Biden is scheduled to travel to Brussels next week for talks with NATO and European leaders to discuss the Russian invasion, White House Press Secretary Jen Psaki said Tuesday.

In an emotional speech to lawmakers in Canada, Zelenskyy asked the Canadian Parliament and Prime Minister Justin Trudeau to help create a no-fly zone over Ukraine. The Ukrainian president spoke by video to a packed House of Commons chamber in Ottawa.

WHAT ABOUT SANCTIONS AGAINST RUSSIA?

The U.S. added more sanctions Tuesday, whose targets include senior Russian military officials. The U.S. also placed additional sanctions on Belarus leader Alexander Lukashenko for allowing Russia to use his country as a staging ground for attacks on Ukraine.

The EU also added new sanctions to deny oligarchs luxuries such as purebred horses and sanctioned 15 individuals, including the chief executive of Russia’s state-run television station Channel One, which the EU says is used to spread propaganda.

HOW IS THE SPORTS WORLD BEING AFFECTED BY RUSSIA’S WAR IN UKRAINE?

The EU imposed sanctions Tuesday on Chelsea soccer club owner Roman Abramovich. Britain had already frozen Abramovich’s assets and prevented Chelsea from selling new tickets or merchandise or signing new players.

The Court of Arbitration for Sport upheld a ban on Russian soccer teams from participating in European competition. Russia is also asking CAS to review a similar ban by FIFA, which awarded Poland a bye in its scheduled March 24 World Cup qualifying match against Russia.

The Swiss swimming federation is threatening to boycott this year’s world championships in Budapest, Hungary in June and July if the sport’s governing body allows Russian and Belarusian athletes to compete. FINA, the International Swimming Federation, has said it opposes a ban and would allow them to compete without their national flags.

Wimbledon organizers and the British government are discussing whether Russian tennis players should be allowed to compete at this year’s tournament if they don’t distance themselves from President Vladimir Putin.

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Follow the AP’s coverage of the war between Russia and Ukraine: http://apnews.com/hub/russia-ukraine