KYIV, Ukraine — What looked like a breakthrough cease-fire to evacuate residents from two cities in Ukraine quickly fell apart Saturday as Ukrainian officials said shelling had halted the work to remove civilians hours after Russia announced the deal.

The Russian defense ministry earlier said it had agreed on evacuation routes with Ukrainian forces for Mariupol, a strategic port in the southeast, and the eastern city of Volnovakha. The vaguely worded statement did not make clear how long the routes would remain open.

“The Russian side is not holding to the cease-fire and has continued firing on Mariupol itself and on its surrounding area,” said Kyrylo Tymoshenko, the deputy head of President Volodymyr Zelenskyy’s office. “Talks with the Russian Federation are ongoing regarding setting up a cease-fire and ensuring a safe humanitarian corridor.”

Russia breached the deal in Volnovakha as well, Deputy Prime Minister Iryna Vereshchuk told reporters. “We appeal to the Russian side to stop firing,” she said. Meanwhile, Moscow outlet RIA Novosti carried a Russian defense ministry claim that the firing came from inside both cities against Russian positions.

The struggle to enforce the cease-fire showed the fragility of efforts to stop fighting across Ukraine as people continued to flee the country on the 10th day after Russian forces invaded.

Mariupol had been the scene of growing misery in recent days amid an assault that knocked out power and most phone service and raised the prospect of food and water shortages for hundreds of thousands of people in freezing weather. Pharmacies are out of medicine, Doctors Without Borders said.

A top official in Mariupol, Pavlo Kirilenko, the head of the Donetsk military-civil administration that includes the city, had said the humanitarian corridor would extend to Zaporizhzhia, 226 kilometers (140 miles) away.

In comments carried on Ukrainian television, Mariupol Mayor Vadym Boychenko said thousands of people had gathered for safe passage out of the city and buses were departing when shelling began.

“We value the life of every inhabitant of Mariupol and we cannot risk it, so we stopped the evacuation,” he said.

Before Russia announced the limited cease-fire, Ukraine had urged Moscow to create humanitarian corridors to allow children, women and the older adults to flee the fighting, calling them “question No. 1.”

A bright flaring object lands in the grounds of the nuclear plant in Enerhodar, Ukraine, early Friday. Zaporizhzhia nuclear power plant via Associated Press

Diplomatic efforts continued as U.S. Secretary of State Antony Blinken arrived in Poland to meet with the prime minister and foreign minister, a day after attending a NATO meeting in Brussels in which the alliance pledged to step up support for eastern flank members.

Aeroflot, Russia’s flagship state-owned airline, announced that it plans to halt all international flights. except to Belarus, starting Tuesday in the wake of Western sanctions imposed on Russia. The country’s aviation agency, Rosaviatsiya, had recommended that all Russian airlines with foreign-leased planes halt passenger and cargo flights abroad to prevent the aircraft from being impounded.

As Russian forces batter strategic locations in Ukraine, Zelenskyy has lashed out at NATO for refusing to impose a no-fly zone over his country, warning that “all the people who die from this day forward will also die because of you.”

NATO has said a no-fly zone, which would bar all unauthorized aircraft from flying over Ukraine, could provoke widespread war in Europe with nuclear-armed Russia. But as the United States and other NATO members send weapons for Kyiv and more than 1 million refugees spill through the continent, the conflict is already drawing in countries far beyond Ukraine’s borders.

Russia continues to crack down on independent media reporting on the war, also blocking Facebook and Twitter, and more outlets say they are pausing their work inside the country.

And in a warning of a hunger crisis yet to come, the U.N. World Food Program has said millions of people inside Ukraine, a major global wheat supplier, will need food aid “immediately.

Ukraine’s president was set to brief U.S. senators Saturday by video conference as Congress considers a request for $10 billion in emergency funding for humanitarian aid and security needs.

In a video message to antiwar protesters in several European cities, Zelenskyy appealed for help. “If we fall, you will fall,” he said.

The U.N. Security Council scheduled an open meeting for Monday on the worsening humanitarian situation. The United Nations estimates that 12 million people in Ukraine and 4 million fleeing to neighboring countries in the coming months will need humanitarian aid.

Russia’s attack on Friday on Ukraine’s largest nuclear power plant, in Zaporizhzhia, caused global alarm, but Russian forces did not make significant progress in their offensive to sever Ukraine’s access to the Black Sea and the Sea of Azov, which would deal a severe blow to the country’s economy.

A vast Russian armored column threatening Ukraine’s capital remained stalled outside Kyiv, but Russia’s military has launched hundreds of missiles and artillery attacks on cities and other sites across the country.

As homes in the northern city of Chernihiv burned from what locals described as Russian shelling, one resident accused Europe of merely looking on. “We wanted to join NATO and the EU and this is the price we are paying, and NATO cannot protect us,” she said.

People who left Ukraine wait for a bus to take them to the train station in Przemysl, at the border crossing in Medyka, Poland, on Friday. Associated Press/Visar Kryeziu

More than 840 children have been wounded in the war, and 28 have been killed, according to Ukraine’s government. A total of 331 civilians had been confirmed killed in the invasion, but the true number is probably much higher, the U.N. human rights office said.

In Romania, one newly arrived refugee, Anton Kostyuchyk, struggled to hold back tears as he recounted leaving everything behind in Kyiv and sleeping in churches with his wife and three children during their journey out.

“I’m leaving my home, my country. I was born there, and I lived there,” he said. “And what now?”

Appearing on video in a message to antiwar protesters in several European cities, Zelenskyy continued to appeal for help.

“If we fall, you will fall,” he said. “And if we win, and I’m sure we’ll win, this will be the victory of the whole democratic world. This will be the victory of our freedom. This will be the victory of light over darkness, of freedom over slavery.”

Kyiv’s central train station remained crowded with people desperate to join the more than 1.4 million who have fled Ukraine. “People just want to live,” one woman, Ksenia, said.

A destroyed armored personnel carrier stands in the central square of the town of Makariv, 60 miles west of Kyiv, after a heavy night battle on Friday. Efrem Lukatsky/Associated Press

Ukrainian presidential adviser Oleksiy Arestovich said battles involving airstrikes and artillery continued northwest of Kyiv, and the northeastern cities of Kharkiv and Okhtyrka came under heavy fire.

He said Ukrainian forces were still holding the northern city of Chernihiv and the southern city of Mykolaiv. Ukrainian artillery also defended Ukraine’s biggest port city, Odesa, from repeated attempts by Russian ships, Arestovich said.

Another strategic port, Mariupol, on the Sea of Azov, was “partially under siege,” and Ukrainian forces were pushing back efforts to surround the city, Arestovich said.

Amid the warfare, there were occasional signs of hope.

As explosions sounded on the fringes of Kyiv, Dmytro Shybalov and Anna Panasyk smiled and blushed at the civil registry office where they married Friday. They fell in love in 2015 in Donetsk amid the fighting between pro-Russian separatists and Ukrainian forces that was a precursor to the countrywide war.

“It’s 2022 and the situation hasn’t changed,” Shybalov said. “It’s scary to think what will happen when our children will be born.”

Karmanau reported from Lviv, Ukraine. Chernov reported from Mariupol, Ukraine. Sergei Grits in Odesa, Ukraine; Jamey Keaten in Geneva; Vanessa Gera in Warsaw, Poland; Frank Jordans in Berlin; Matt Sedensky in New York; Robert Burns in Washington; and other AP journalists from around the world contributed to this report.