Ukraine's second-largest city, Kharkiv, came under intense rocket fire Monday as Ukrainian and Russian officials meet for peace talks near Ukraine’s border with Belarus.
Dozens have reportedly been killed in the city and hundreds are injured, local media reports. A Ukrainian official also posted to Facebook that the city was "massively shelled with Grad multiple rocket launchers."
"Dozens of dead and hundreds of wounded! This horror must be seen by the whole world! Death to the occupiers!" Anton Gerashchenko, adviser to the Minister of Internal Affairs of Ukraine, wrote on his Facebook page on Monday.
A delegation of Ukrainian officials arrived near the Pripyat River Monday on a helicopter to begin peace talks with their Russian counterparts.
Ukrainian President Volodymyr Zelenskyy, who will remain in Kyiv during the peace talks, told UK Prime Minister Boris Johnson on a call Sunday that the next 24 hours will be crucial for his country, according to a Downing Street spokesperson.
The talks come after Russian forces reportedly captured two small cities in southeastern Ukraine, according to Russian Defense Ministry spokesman Igor Konashenkov.
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"The Russian Armed Forces have taken control of Berdyansk and Enerhodar," Konashenkov said at a press briefing Monday.
Belarus is also expected to send troops into Ukraine as soon as Monday to fight alongside Russian forces, according to a senior U.S. intelligence official.
Monday marks the fifth day of fighting between the nations since Russia invaded Ukraine last week. Ukrainian fighters have maintained control of the capital of Kyiv.
The mayor of Kyiv Vitali Klitschko praised the "patriotic" residents of the city and said he is unshaken despite Russian forces trying to gain control of the city.
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"We show our character, our knowledge, our values," the mayor said. "To be honest, we don’t have 100% control. We built this territorial defense (system) in a short amount of time — but these are patriotic people."
Tensions flared Sunday morning when Putin raised the alert status for his nuclear forces to "special regime of combat duty," threatening the fighting could escalate into a nuclear war.
U.S. Ambassador to the United Nations Linda Thomas-Greenfield said Sunday on CBS's "Face the Nation" that Putin's order is an unacceptable escalation.
"It means that President Putin is continuing to escalate this war in a manner that is totally unacceptable and we have to continue to stem his actions in the strongest possible way," she said.
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On Monday, Zelenskyy asked the European Union to fast-track Ukraine for membership, citing the country’s goal to be "equal."
"Our goal is to be with all Europeans and, most importantly, to be equal. I'm sure that's fair. I am sure we deserve it," he said in a video speech shared on social media.
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The number of Ukrainian refugees has meanwhile increased, with the UN’s refugee agency saying more than 500,000 refugees have fled the nation to neighboring countries. The number is up from the agency’s estimate on Sunday of 368,000 Ukrainians.