Ukrainian and Russian delegations resume peace talks Monday, a day after Russia launched a lethal cruise missile attack on a western Ukraine military base just 25 kilometers from Poland, a NATO member. At least 35 people died and 134 were wounded in the attack on the International Center for Peacekeeping and Security.
Ukraine President Volodymyr Zelenskyy said Sunday in his daily nighttime address that Sunday was a "black day" for the country because of the attack.
The president said he had given a "clear warning" to Western leaders about the likelihood of an attack at the base where NATO units train with Ukrainian troops.
"This does not come as a surprise to the American intelligence and national security community," U.S. National Security Advisor Jake Sullivan said during a Sunday appearance on CNN. "What it shows is that Vladimir Putin is frustrated by the fact that his forces are not making the kind of progress that he thought that they would make."
"If Russia attacks, fires upon, takes a shot at NATO territory, the NATO alliance would respond to that," warned Sullivan in an interview on the CBS network's "Face the Nation" program.
President Zelenskyy Sunday night said he has attempted to arrange a meeting with Putin, but has been unsuccessful even though Ukranian and Russian delegations talk every day to make arrangements for humanitarian corridors and ceasefire agreements.
Meanwhile, Sullivan and officials from the National Security Council and State Department are scheduled to meet Monday in Rome with Chinese Communist Party Politburo Member and Director of the Office of the Foreign Affairs Commission Yang Jiechi.
The discussion will be "part of our ongoing efforts to maintain open lines of communication between the United States and the People's Republic of China (PRC). The two sides will discuss ongoing efforts to manage the competition between our two countries and discuss the impact of Russia's war against Ukraine on regional and global security," according to NSC spokesperson Emily Horne.
Media reports emerged Sunday that Moscow has requested military and economic assistance from China for Russia's war in Ukraine. Earlier, the White House warned China of severe "consequences" if it helps Russia avoid sanctions.
Sullivan on Sunday also responded to growing concern Russia will use chemical weapons in Ukraine.
"We can't predict a time and place," said Sullivan on CBS, noting an escalation of rhetoric from Moscow falsely accusing the United States and Ukraine of developing chemical or biological weapons to use against Russian troops.
"That's an indicator that the Russians are getting ready to do it" and blame it on others, according to Sullivan.
On NBC's "Meet the Press," Sullivan said, "We've consulted with our allies and partners about it, and we are prepared for that eventuality." He echoed U.S. President Joe Biden's warning from last week that Russia would face severe consequences if such weapons are deployed.
Ukraine's human rights ombudswoman says the Russians used a phosphorus munition in an overnight attack on the eastern Ukrainian city of Popasna in the Luhansk region. VOA was not immediately able to verify the claim. While phosphorus is not considered a chemical weapon, its use against human beings is banned under international law.
In a video released shortly early Monday local time, Ukrainian President Volodymyr Zelenskyy renewed a plea for NATO to impose a no-fly zone over his country, predicting if that does not happen "it is only a matter of time before Russian rockets fall on your territory, on NATO territory."
In recent days, satellite imagery and media reporters have indicated Russian armored units are poised to relaunch a major offensive to attempt to take Kyiv, the capital of Ukraine, after a lull.
An award-winning American filmmaker and journalist is among the latest casualties of the conflict near the capital.
Brent Renaud died in Irpin, a suburb of Kyiv, according to officials.
"It is one more example of the brutality of Vladimir Putin and his forces as they've targeted schools and mosques and hospitals and journalists," said Sullivan on CNN's "State of the Union" program.
Renaud, who had previously worked for The New York Times, NBC and HBO, "paid with his life for attempting to expose the insidiousness, cruelty and ruthlessness of the aggressor," said a statement from Anton Gerashchenko, an adviser to Ukraine's interior minister.
In recent days, the focus of the invasion has shifted to the besieged southeastern Ukrainian port city of Mariupol.
"We have already evacuated almost 125,000 people to the safe territory through humanitarian corridors," President Zelenskyy said in a video address released earlier Sunday. "We're doing everything to counter occupiers who are even blocking Orthodox priests accompanying this aid, food, water and medicine. There are 100 tons of the most necessary things that Ukraine sent to its citizens."
Jeff Seldin and Cindy Saine contributed to this report. Some information also came from The Associated Press, Agence France-Presse and Reuters.