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

Management of Ukraine's Zaporizhzhya Nuclear Power Plant in southeastern Ukraine, Europe's largest nuclear power plant, is now operating under orders from the commander of the Russian forces that took control of the site last week, the International Atomic Energy Agency said Sunday.

IAEA Director-General Rafael Mariano Grossi warned that the Russian takeover of the plant violates an indispensable pillar of nuclear safety in which operating staff must be able to fulfill their safety and security duties and make decisions free of undue pressure.

The IAEA also said it has been informed by Ukraine's nuclear regulator that Russian forces have switched off some mobile networks and the internet so that reliable information from the site cannot be obtained through normal channels of communication. The regulator told the IAEA that staff operating at Zaporizhzhya are having major problems communicating outside of the plant because phone lines, email service and fax machines are no longer functioning.

Despite the communication issues, the regulator was able to provide updated information about the operational status of the Zaporizhzhya plant, confirming radiation levels there remain normal.

"I'm extremely concerned about these developments that were reported to me today. Just a few days after I presented the seven main elements of nuclear safety and security to the IAEA Board, several of them are already being compromised," Grossi said. "In order to be able to operate the plant safely and securely, management and staff must be allowed to carry out their vital duties in stable conditions without undue external interference or pressure."

Grossi added, "The deteriorating situation regarding vital communications between the regulator and the Zaporizhzhya NPP is also a source of deep concern, especially during an armed conflict that may jeopardize the country’s nuclear facilities at any time. Reliable communications between the regulator and the operator are a critical part of overall nuclear safety and security."

The nuclear regulator also reported that it is having problems communicating with personnel at the decommissioned Chornobyl Nuclear Power plant, the site of a 1986 nuclear disaster, saying only email communication is possible for now. The staff of more than 200 technical personnel and guards have not been able to rotate since Feb 23.

ABC News' Christine Theodorou

The United Nations High Commissioner for Human Rights reported Sunday that it has verified 1,123 civilian casualties in Ukraine since the Russian invasion of the country began on Feb. 24.

The OHCHR said the casualties include 364 civilians that have been killed, including 25 children. Another 759 civilians have been injured in the fighting, including 41 children, the OHCHR reported.

OHCHR said it is only reporting verified civilian casualties and acknowledged that the real figures are likely "considerably higher."

Most of the civilian casualties recorded were caused by the use of explosive weapons with a wide impact area, including shelling from heavy artillery and multi-launch rocket systems, and missile and airstrikes.

At least 503 of the civilian casualties have occurred in the heavily Russian-controlled Donetsk and Luhansk provinces of eastern Ukraine's Donbas region, including 88 deaths. Another 374 civilian casualties, including 65 deaths, have occurred in the Ukrainian government-controlled areas of the Donbas region.

OHCHR reported that in other regions of Ukraine -- including the cities of Kyiv, Cherkasy, Chernihiv, Kharkiv, Kherson, Mykolaiv, Odesa, Sumy, Zaporizhzhia and Zhytomyr -- 276 civilians have died and 344 have been injured.

ABC News' Christine Theodorou

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