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

More than 1.5 million people have fled Ukraine since the Russian invasion began, the head of the U.N. Refugee Agency said on Sunday.

"More than 1.5 million refugees from Ukraine have crossed into neighbouring countries in 10 days -- the fastest growing refugee crisis in Europe since World War II," Filippo Grandi, the U.N. high commissioner for refugees, said on Twitter.

An official in Mariupol, a Ukrainian city besieged by the Russians, said a cease-fire on Sunday will allow citizens to evacuate.

The temporary cease-fire was scheduled to begin at 10 a.m. local time, with an evacuation starting two hours later, Pavlo Kyrylenko, governor of Donetsk Oblast, said on Facebook.

A similar plan had been announced for Saturday, but Russian shells continued to fall throughout the day.

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