Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

Russian forces resumed shelling the Azovstal steel plant in Mariupol on Sunday after some civilians inside the facility and in nearby homes were evacuated during a brief cease fire, according Ukrainian officials.

"They are shelling the plant with all kinds of weapons," said Denis Schlega, commander of the 12th Brigade of Operational Assignment in Mariupol.

Earlier Sunday, Ukrainian President Volodymyr Zelenskyy, the International Committee of the Red Cross, the United Nations and Russian Ministry of Defense all confirmed that some civilians were evacuated from the steel plant, where a Ukrainian military unit is making a last stand in the port city that is almost entirely under Russian control.

Zelenskyy said about 100 civilians were evacuated from the steel plant on Sunday and were being taken to Zaporizhia, a city under Ukrainian control.

The Mariupol City Council said in a statement that evacuations from Mariupol had stopped Sunday afternoon due to "security reasons." The city council said the evacuations would resume on Monday.

At least three civilians were killed and eight others injured on Sunday as a result of heavy shelling from Russian forces in the Kharkiv region in northeast Ukraine, according to a Ukrainian official.

The casualties were reported in the residential areas of Saltivka, Bohodukhiv and Zolochif, according to Oleg Sinegubov, head of the Kharkiv Regional Military Administration.

-ABC News' Christine Theodorou

Pope Francis on Sunday described the war in Ukraine as a "macabre regression of humanity" that makes him "suffer and cry."

Speaking to thousands of people crowded into St. Peter's Square at the Vatican, the pope called for humanitarian corridors to be opened to evacuate civilians trapped inside or near a steel plant in the Ukrainian port city of Mariupol.

Evacuation of civilians at the Azovstal steel plant, where Ukrainian forces have been staging a last stand against Russian troops, have started, Ukrainian President Volodymyr Zelenskyy, the Red Cross and the Russian Ministry of Defense confirmed on Sunday.

During Sunday's Vatican service, Francis repeated his criticism of Russia for invading Ukraine.

"My thoughts go immediately to the Ukrainian city of Mariupol, the city of Mary, barbarously bombarded and destroyed," the pontiff said of the Russian-controlled southeastern port city, which is named after Mary. "I suffer and cry thinking of the suffering of the Ukrainian population, in particular the weakest, the elderly, the children."

In Catholicism, the month of May is dedicated to Mary, the mother of Jesus. Francis asked for monthlong prayers for peace in Ukraine.

"While we are witnessing a macabre regression of humanity, I ask you, together with so many anguished people, if we are really seeking peace, if there is the will to avoid a continuous military and verbal escalation, if we are doing everything possible to make the weapons stop? Please, let us not give in to the logic of violence, to the perverse spiral of arms. Let us take the path of dialogue and peace. Let us pray."

-ABC News' Rashid Haddou

Some civilians who have been holed up in houses near fighting being waged at a steel plant in the Ukrainian city of Mariupol were evacuated via a humanitarian corridor established on Saturday and Sunday, according to the Russian Ministry of Defense.

At least 46 people were allowed out of the heavily bombed port city when they emerged from houses near the Azovstal steel plant, where Ukrainian forces have been staging a last stand against Russian troops ringing the facility, the Russian Ministry of Defense said Sunday.

The civilians emerged from their houses during a period of calm in the fighting at the steel plant, according to the Russian military.

"Twenty-five local residents came out in the afternoon of April 30. At nightfall, taking the advantage of the regime of calm, a second group of 21 people came out and was taken to the populated locality of Bezimenne," the Russian Defense Ministry said.

The two groups of civilians came out "as a result of establishing a regime of calm and opening a humanitarian corridor from the residential houses nearest to the grounds of the Azovstal integrated steel works," the defense ministry's statement said.

Ukrainian President Volodymyr Zelenskyy confirmed on Twitter Sunday that the "evacuation of civilians from Azovstal began." Zelenskyy said about 100 civilians were evacuated from the plant on Sunday and that the U.N. is working on evacuating others.

A Red Cross representative told the Associated Press at least 20 civilians were evacuated from the Azovstal steel plant amid a temporary cease-fire observed by Ukrainian and Russian forces. A journalist for the AP reported seeing women and children arriving in Bezimenne, which is controlled by Russian-backed separatists in eastern Ukraine.

The AP reported the newly arriving evacuees were placed in a refugee tent camp and are expected to be escorted to the Ukrainian-controlled city of Zaporizhzhia by U.N. and Red Cross vehicles.

Several previous attempts to establish humanitarian corridors out of Mariupol have failed. Ukrainian officials claimed the previous evacuation were not successful because Russian troops did not follow through with the planned ceasefires.