LVIV, UKRAINE -- Russia bombarded cities across Ukraine on Saturday, pounding Mariupol in the south, shelling the outskirts of the capital, Kyiv, and thwarting the efforts of people trying to flee the violence.

In Mariupol, which has endured some of the worst punishment since Russia invaded, efforts to bring food, water and medicine into the port city of 430,000 and to evacuate civilians, were prevented by unceasing attacks. More than 1,500 people have died in Mariupol during the siege, according to the mayor's office, and the shelling has even interrupted efforts to bury the dead in mass graves.

Talks aimed at reaching a cease-fire again failed Saturday, and while the U.S. announced plans to provide another $200 million to Ukraine for weapons, a senior Russian diplomat warned that Moscow could attack foreign shipments of military equipment.

Ukrainian President Volodymyr Zelensky accused Russia of trying to break his country apart, as well as starting "a new stage of terror" with the alleged detention of a mayor from a city west of Mariupol.

"Ukraine will stand this test. We need time and strength to break the war machine that has come to our land," Zelensky said during his nightly address to the nation Saturday.

Russian soldiers pillaged a humanitarian convoy that was trying to reach Mariupol and blocked another, a Ukrainian official said. Ukraine's military said Russian forces captured Mariupol's eastern outskirts, tightening their siege of the strategic port. Taking Mariupol and other ports on the Azov Sea could allow Russia to establish a land corridor to Crimea, which it seized from Ukraine in 2014.

An Associated Press journalist in Mariupol witnessed tanks firing on a nine-story apartment building and was with a group of hospital workers who came under sniper fire on Friday. A worker shot in the hip survived, but conditions in the hospital were deteriorating: Electricity was reserved for operating tables, and people with nowhere else to go lined the hallways.

Among them was Anastasiya Erashova, who wept and trembled as she held a sleeping child. Shelling had just killed her other child as well as her brother's child, Erashova said, her scalp crusted with blood.

"No one was able to save them," she said.

In Irpin, a suburb about 12 miles (20 kilometres) northwest of central Kyiv, bodies lay out in the open Saturday on streets and in a park.

"When I woke up in the morning, everything was covered in smoke, everything was dark. We don't know who is shooting and where," resident Serhy Protsenko said as he walked through his neighbourhood. Explosions sounded in the distance. "We don't have any radio or information."

Zelensky encouraged his people to keep up their resistance.

"We do not have the right to let up our defence, no matter how difficult it may be," he said. Later Saturday, Zelensky reported that 1,300 Ukrainian soldiers had died since the Russian invasion began Feb. 24.

The first major city to fall, earlier this month, was Kherson, a vital Black Sea port of 290,000 residents. Zelensky said Saturday that Russians were using blackmail and bribery in an attempt to force local officials to form a "pseudo-republic" in the southern Kherson region, much like those in Donetsk and Luhansk, two eastern regions where pro-Russian separatists began fighting Ukrainian forces in 2014. One of the pretexts Russia used to invade was that it had to protect the separatist regions.

Zelensky again deplored NATO's refusal to declare a no-fly zone over Ukraine and said Ukraine has sought ways to procure air defence assets, though he didn't elaborate. U.S. President Joe Biden announced another $200 million in aid to Ukraine, with an additional $13 billion included in a bill that has passed the House and should pass the Senate within days. NATO has said that imposing a no-fly zone could lead to a wider war with Russia.

The Ukrainian president also accused Russia of detaining the mayor of Melitopol, a city 192 kilometres (119 miles) west of Mariupol. The Ukrainian leader called on Russian forces to heed calls from demonstrators in the occupied city for the mayor's release.

In multiple areas around Kyiv, artillery barrages sent residents scurrying for shelter as air raid sirens wailed. Britain's Defence Ministry said Russian forces that had been massed north of the capital had edged to within 25 kilometres (15 miles) of the city center and spread out, likely to support an attempted encirclement.

A convoy of hundreds of people fleeing Peremoha, about 20 kilometres (12 miles) northeast of Kyiv, were forced to turn back under shelling by Russian forces that killed seven people, including a child, Ukraine's defence ministry said Saturday. Moscow has said it would establish humanitarian corridors out of conflict zones, but Ukrainian officials have accused Russia of disrupting those paths and firing on civilians.

Ukraine's Deputy Prime Minister Iryna Vereshchuk said just nine of 14 agreed-upon corridors were open on Saturday, and that about 13,000 people had used them to evacuate around the country.

Ukraine's military and volunteer forces have been preparing for an all-out assault on the capital. Kyiv Mayor Vitali Klitschko said Thursday that about 2 million people, half the metropolitan area's inhabitants, had left and that "every street, every house ΓǪ is being fortified."

Zelensky said Saturday that Russia would need to carpet-bomb Kyiv and kill its residents to take the city.

"They will come here only if they kill us all," he said. "If that is their goal, let them come."

French and German leaders spoke Saturday with Russian President Vladimir Putin in a failed attempt to reach a cease-fire. According to the Kremlin, Putin laid out terms for ending the war. For ending hostilities, Moscow has demanded that Ukraine drop its bid to join NATO and adopt a neutral status; acknowledge the Russian sovereignty over Crimea, which it annexed from Ukraine in 2014; recognize the independence of separatist regions in the country's east; and agree to demilitarize.

In Mariupol, where electricity, gas and water supplies have been knocked out, aid workers and Ukrainian authorities described an unfolding humanitarian catastrophe. Aid group Doctors Without Borders said residents are dying from a lack of medication and are draining heating pipes for drinking water.

Russian forces have hit at least two dozen hospitals and medical facilities, according to the World Health Organization.

The Russian invaders appear to have struggled far more than expected against determined Ukrainian fighters. Still, Russia's stronger military threatens to grind down Ukrainian forces.

Russian Deputy Foreign Minister Sergei Ryabkov warned on Saturday that his country could attack foreign shipments of military equipment to Ukraine. He said sending equipment is "an action that makes those convoys legitimate targets."

Thousands of soldiers on both sides are believed to have been killed along with many civilians, including at least 79 Ukrainian children, its government says. At least 2.5 million people have fled the country, according to the United Nations refugee agency.

One is Elena Yurchuk, a nurse from the northern city of Chernihiv. She was in a Romanian train station Saturday with her teenage son, Nikita, unsure whether their home was still standing.

"We have nowhere to go back to," said Yurchuk, 44, a widow who hopes to find work in Germany. "Nothing left."

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Karmanau reported from Lviv, Ukraine. Associated Press journalists Felipe Dana, Andrea Rosa in Irpin, Andrew Drake in Kyiv and other reporters around the world contributed.