KYIV, Ukraine (AP) -- Russia's relentless bombardment of Ukraine edged closer to central Kyiv on Tuesday, with a series of strikes hitting a residential neighborhood as the leaders of three European Union countries planned a bold visit to Ukraine's embattled capital in a show of support.
Shortly before dawn, large explosions thundered across Kyiv from what Ukrainian authorities said was artillery strikes. The shelling ignited a huge fire and a frantic rescue effort in a 15-story apartment building in a western district of the city. At least one person was killed in the blast.
Shockwaves from an explosion also damaged the entry to a downtown subway station that has been used as a bomb shelter. City authorities tweeted an image of the blown-out facade, saying trains would no longer stop at the station.
As Russia stepped up its assault on Kyiv, the leaders of Poland, the Czech Republic and Slovenia announced they would travel to Ukraine's capital Tuesday on a European Union mission to show support for the country
"The aim of the visit is to express the European Union's unequivocal support for Ukraine and its freedom and independence," Czech Prime Minister Petr Fiala said in a tweet.
He will be joined by Slovenian Prime Minister Janez JanÅ¡a, Polish Prime Minister Mateusz Morawiecki and Jaroslaw Kaczynski, who is Poland's deputy prime minister for security and the leader of the conservative ruling party.
Russian and Ukrainian negotiators also planned to hold a second day of talks as Russia's invasion of Ukraine entered its 20th day. The Red Cross and the United Nations refugee agency say millions of people face food and medicine shortages along with the immediate conflict threats of shelling and air attacks.
The International Organization for Migration reported that the number of people who have fled Ukraine since Russia invaded on Feb. 24 passed 3 million on Tuesday. The U.N. has described the flood of people crossing into Poland and other neighboring countries as Europe's biggest refugee crisis since World War II.
When Russia launched the war nearly three weeks ago, fear of an imminent invasion gripped the Ukrainian capital, and residents slept in subway stations or crammed onto trains to flee. But as the Russian offensive bogged down, Kyiv saw a relative lull.
Fighting has intensified on the city's outskirts in recent days, and sporadic air raid sirens ring out around the capital.
Tuesday's early morning artillery strikes hit the Svyatoshynskyi district of western Kyiv, adjacent to the suburb of Irpin, which has seen some of the worst battles of the war.
Flames shot out of the 15-story apartment building and smoke choked the air as firefighters climbed ladders to rescue people. The assault blackened several floors of the building, ripped a hole in the ground outside and blew out windows in neighboring apartment blocks.
A firefighter at the scene confirmed one person had died and that several had been rescued, but others remained inside as rescuers tried to reach them.
A 10-story apartment building in the Podilsky district of Kyiv, north of the government quarter, also was damaged by unspecified ammunition. Russian forces also stepped up strikes overnight on Irpin and the northwest Kyiv suburbs of Hostomel and Bucha, said the head of the capital region, Oleksiy Kuleba.
"Many streets (in those areas) have been turned into a mush of steel and concrete. People have been hiding for weeks in basements, and are afraid to go out even for evacuations," Kuleba said on Ukrainian television.
Russian forces also stepped up their attacks on Ukraine's second-largest city, Kharkiv in the east, with more than 60 strikes overnight, according to regional administration chief Oleh Sinehubov.
"Fires are raging in the city, and there are not enough firefighters," he said.
The strikes hit the city's historical center, including the main marketplace and Gagarin Avenue, a major thoroughfare.
Rescuers have pulled out "dozens of bodies of civilian residents," from the ruins of destroyed apartment buildings, he said on Ukrainian television.
Ukrainian President Volodymyr Zelenskyy is seeking to extend martial law until April 24 and to require men ages 18 to 60 to stay in the country to fight. Zelenskyy submitted the extension in a bill to parliament, which is expected to vote on it this week.
Talks between Russian and Ukrainian negotiators were due to resume Tuesday, after failing to make a break through -- or to break down -- on Monday. The two sides had expressed some optimism about the negotiations, which Ukrainian presidential aide Mykhailo Podolyak said would discuss "peace, ceasefire, immediate withdrawal of troops & security guarantees."
Russia's military is bigger and better equipped than Ukraine's, but its troops have faced stiffer-than-expected resistance, bolstered by arms supplied by the West.
U.S. officials said Russian troops made little progress on the ground in recent days and were still about 15 kilometers (9 miles) from the center of Kyiv as of Monday. The Pentagon said Russian forces have launched more than 900 missiles but not taken control of the air above Ukraine.
U.S. administration officials alleged that China had signaled to Moscow that it would be willing to provide both military support in Ukraine and financial backing to help stave off effects of Western sanctions.
U.S. national security adviser Jake Sullivan warned China against helping Russia during a meeting in Rome on Monday with a senior Chinese diplomat. The Kremlin denied asking China for military equipment to use in Ukraine.
With each day, the human cost of the grinding war continues to rise. The Ukrainian general prosecutor's office released details of two deadly Russian attacks that took place Monday: an artillery strike that hit a university and open-air market in the northern city of Chernihiv, killing 10, and the shooting of a 65-year-old woman on a bus that was evacuating civilians from a Kyiv suburb.
The number of people killed in a Russian rocket attack on a TV tower in western Ukraine on Monday rose to 19, authorities in the Rivne region said Tuesday. The Rivne regional government posted on its Facebook page that 19 people were killed and nine were injured in the strike on the TV tower in Antopol, a village that is about 160 kilometers (100 miles) from the border of NATO member Poland.
A Russian airstrike near a Ukrainian checkpoint caused extensive damage to a downtown Kyiv neighborhood, killing one person, Ukraine's emergency agency said.
Kateryna Lot said she was in her apartment as her child did homework when they heard a loud explosion and ran to take shelter.
"The child became hysterical. Our windows and the balcony were shattered. Part of the floor fell down," she said. "It was very, very scary."
In an area outside Kyiv, Fox News reporter Benjamin Hall was injured while reporting and was hospitalized, the network said.
There was a rare glimmer of hope in the encircled port city of Mariupol after a convoy of 160 civilian cars left along a designated humanitarian route, the city council reported Monday. Over the past 10 days or so, the lethal siege has pulverized homes and other buildings and left people desperate for food, water, heat and medicine.
Previous attempts to evacuate civilians and deliver humanitarian aid to the southern city of 430,000 were thwarted by fighting.
Ukraine's military said it repelled an attempt Monday to take control of Mariupol by Russian forces, who were forced to retreat. Satellite images from Maxar Technologies showed fires burning across the city, with many high-rise apartment buildings heavily damaged or destroyed.
Ukraine claims its forces have killed 150 Russian troops and destroyed two Russian tanks in the battle for Mariupol.
The Kremlin-backed leader of the Russian region of Chechnya said on a messaging app that Chechen fighters were spearheading the offensive on Mariupol.
Elsewhere, the Russian military said 20 civilians in the separatist-controlled city of Donetsk in eastern Ukraine were killed by a ballistic missile launched by Ukrainian forces. The claim could not be independently verified.
In Russia, the live main evening news program on state television was briefly interrupted by a woman who walked into the studio holding a poster against the war. The OVD-Info website that monitors political arrests identified her as a Channel 1 employee and said she was taken into police custody.
The U.N. refugee agency said Sunday that it had recorded at least 596 civilian deaths since Russia invaded Ukraine on Feb. 24, though it believes the true toll is much higher.