The U.S. Embassy in Kyiv issued a security alert Saturday warning that a “potentially significant air attack” could hit the city in the next 24 hours.

The U.S. Mission Ukraine said in a statement, “The U.S. embassy in Kyiv has received information concerning a potentially significant air attack that may occur at any time over the next 24 hours.

“The embassy, as always, recommends U.S. citizens be prepared to immediately shelter in the event an air alert is announced.”

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The embassy urged Americans to “identify shelter locations before any air alert,” keep reserves of food, water and medication nearby, follow the “directions of Ukrainian officials and first responders in the event of an emergency,” to immediately take shelter if an alert is announced and to download an air raid app like Air Raid Siren or Alarm App. 

By early Sunday morning, the capital was rocked by a massive missile and drone strike, Reuters reported. 

At least three people were injured and some residential buildings were damaged, the mayor said on Telegram. 

The message follows a warning from Ukrainian President Volodmyr Zelenskyy that Russia was preparing to strike Ukraine with a hypersonic Oreshnik missile, citing Ukrainian as well as U.S. and European intelligence. 

“We are seeing signs of preparation for a combined strike on Ukrainian territory, including Kyiv, involving various types of weaponry,” Zelenskyy wrote in an X post Saturday morning. 

“The specified intermediate-range weapons could be used in such a strike. It is important to act responsibly on air-raid alerts, starting this evening. Russian madness truly knows no bounds, so please protect your lives. Use shelters.”

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He added that the use of such weapons would set a precedent for future aggressors. 

“If Russia is allowed to destroy lives on such a scale, then no agreement will restrain other similar hatred-based regimes from aggression and strikes,” he said. “We count on a response from the world and on a response that is not post factum, but preventive. Pressure must be put on Moscow so that it does not expand the war.”

Zelenskyy said Ukraine was preparing its air defenses as much as possible, and “we will respond fully justly to every Russian strike.”

“We have given permission for a parade,” he concluded his post, referring to the President Donald Trump-brokered three-day ceasefire earlier this month, “but Russia has no permission for madness. This war must be ended – we need peace, not some missiles satisfying the sick ambitions of one individual. I thank everyone helping to protect lives. Once again, please take care of yourselves and use shelters tonight.”

At the start of the three-day ceasefire May 9, Russian President Vladimir Putin told reporters he thought the war could come “to an end” soon. 

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On Friday, however, Putin vowed retaliation for a deadly Ukrainian drone strike in Starobilsk, an occupied town in eastern Luhansk, claiming that the Ukrainians hit a college dormitory in a “terrorist” act. 

Ukraine denied the claim, saying it struck a Russian drone command unit in the area.