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

Secretary of State Antony Blinken on Sunday reacted to WNBA star Brittney Griner being detained in Russia, saying “whenever an American is detained anywhere in the world, we of course stand ready to provide every possible assistance and that includes in Russia.”

Blinken noted that he was limited in what he could say, given privacy considerations. He made the comments on Sunday alongside Moldovan President Maia Sandu at a press conference.

He also brought up efforts to seek the release of Paul Whelan and Trevor Reed, two Americas who’ve been detained by Russia.

-ABC News’ Justin Ryan Gomez

U.S. Secretary of State Antony Blinken crossed the border into Ukraine Saturday after meeting with Ukrainian Foreign Minister Dmytro Kuleba at the Korczowa Border Crossing Point.

"The entire world stand with Ukraine," Blinken said, and Kuleba added that he hopes Ukrainians will see this as a "clear manifestation that we have friends who literally stand by us."

Blinken said the sanctions imposed so far against Russia are "producing very, very concrete results" and that the pressure will "grow" until this "war of choice is brought to an end."

When asked directly about helping Kuleba with more firepower, Blinken said, "the support for Ukraine not only has been unprecedented, not only is going to continue, it's going to increase."

Kuleba said Ukraine "appreciates" sanctions that have been announced in the last week, but that more economic and political pressure and "necessary weapons," would "save many lives in Ukraine... many sufferings will be avoided."

Kuleba also said that they are “satisfied" with already arranged supplies of anti-tank weapons and ammunition, but that “it’s no secret” they still want fighter jets and air defense systems.

He also thanked the U.S. for sending stingers, and said they were used on Saturday.

"Just today we shot down three Russian attack aircrafts, which were bombing our cities with the use of stingers but we need -- so to say -- big air defense systems to ensure the safety of our skies. If we lose the skies, there will be much, much more blood on the ground,"Kuleba said.

In response to questions about NATO’s refusal to impose a no-fly zone over Ukraine, Kuleba said it’s a "sign of weakness," but stayed optimistic that they will change their minds.

"The time will come," he said.

-ABC News' Conor Finnegan and Justin Gomez