Russia-Ukraine updates: Putin says 'certain positive movements' in negotiations

A Ukrainian lawmaker confirmed on Sunday that a gas pipeline was damaged in Mariupol, leaving more than 750,000 people in the second-largest city in eastern Ukraine's Donbas region without heat as temperatures plunged to 38 degrees.

Pavlo Kyrylenko, head of the Donetsk region administration, also confirmed Sunday's Mariupol civilian evacuation attempt failed after Russian troops shelled the city, breaking a temporary cease-fire agreement.

"It is extremely dangerous to take people out under such conditions," Kyrylenko wrote in a Facebook post.

Kyrylenko added that a column with a humanitarian cargo is headed to Mariupol from Zaporizhzhia.

Ukrainian lawmaker Inna Sovsun also tweeted a warning of a possible "humanitarian disaster" for nearly 1 million people in Mariupol. Sovsun expressed concern that people could freeze to death considering temperatures in the area often fall below zero this time of the year.

ABC News' Christine Theodorou

Ukraine President Volodymyr Zelenskyy has again appealed to Western countries to impose a "no-fly zone" over his country or send him military aircraft to use against Russia.

Zelenskyy on Sunday referred to an attack on the city of Vinnytsia in west-central Ukraine, saying he saw eight missiles hit an airport there.

"The airport is completely ruined. They deliberately destroy our infrastructure. They hit at our peaceful population. We plead with you every day and urge you again, all the world leaders, help us save lives. Impose a no-fly zone, close our skies. Help stop Russian missiles and aircraft dropping bombs," Zelenskyy said.

He added, "I know you can do it. It's your humanitarian duty to protect life and save lives. If you don't do it, help us with military aircraft! If you don't -- you will share blame for the loss of lives of innocent Ukrainians from now on.”

The Financial Times reported on Saturday night that the United States and Poland are working on a deal for Poland to provide Ukraine with fighter jets, which are Russian-made MiG jets.

-ABC News’ Patrick Reevell

Pope Francis on Sunday again made a strong appeal for peace in Ukraine during his noontime prayer at the Vatican.

“Rivers of blood and tears are flowing in Ukraine. This is not just a military operation, but a war, which sows death, destruction and misery,” the pontiff said from his window overlooking St. Peter’s Square. “The victims are ever more numerous, as are the people fleeing, especially mothers and children. In that tormented country the need for humanitarian assistance grows dramatically from hour to hour.”

People carrying Ukrainian and peace flags listened from the square.

“I make a heartfelt appeal to ensure that humanitarian corridors are in place, and that aid access to the besieged areas is guaranteed and facilitated, in order to offer vital assistance to our brothers and sisters oppressed by bombs and fear,” the pope said.

-ABC News’ Phoebe Natanson

Russia has broken Sunday’s temporary cease-fire in Mariupol, two officials with the mayor’s office told ABC News.

The officials said Russia continued shelling during the first two hours of the cease-fire, which had been scheduled to begin at 10 a.m. local time.

Mariupol officials earlier said an evacuation of residents would begin at noon local time. Sunday’s planned evacuation was to come after a failed cease-fire on Saturday, Ukrainian officials said.

-ABC News’ Matt Gutman