U.S. Closes Its Kyiv Embassy, Warning of Significant Air Attack

The United States Embassy in Kyiv issued an urgent warning on Wednesday morning that Russia might launch “a significant air attack,” closing the embassy and telling employees to shelter in place.

Air-raid alerts are a daily fact of life in Ukraine and the capital often comes under drone and missile attacks, but the embassy rarely issues such a specific alert.

The warning came one day after Ukraine’s military used American-made ballistic missiles to strike into Russian territory for the first time, after receiving long-sought authorization from President Biden to do so. The Kremlin had long warned that such strikes would be treated as an escalation, and on Tuesday vowed to respond.

“We will be taking this as a qualitatively new phase of the Western war against Russia,” Russia’s foreign minister, Sergei V. Lavrov, said at a news conference on Tuesday. “And we will react accordingly.”

In its message on Wednesday, the U.S. Embassy did not offer details about a potential attack, but did not offer details. It urged Americans to pay special attention to air-raid alerts.

An explosion rang out in the capital just before 8 a.m. when air-defense teams shot down a drone, Ukrainian officials said. Falling debris sparked a fire at a multistory residential building. There was no immediate information on casualties.

Such drone attacks have become increasingly common in recent weeks. During 1,000 days of war, Russia has targeted the capital with more than 2,500 missiles and drones, according to data collected by the city’s military administration. Around half of the attacks took place this year.

Since the war began, there have been about 1,370 alerts in Kyiv, according to city officials. Those have lasted more than 1,550 hours in total — meaning that if residents spent every hour of every alert in a shelter, they would have spent more than two months in bunkers.

Many people seek shelter in subways, basements and underground facilities like parking garages when the air-raid warnings wail.

But there is often little warning when ballistic missiles, which travel at several times the speed of sound, are fired at the capital. The time between launch and impact can be minutes.

And many large-scale Russian attacks — like one on Sunday that targeted Ukraine’s power grid — feature a combination of drones, cruises and ballistic missiles aimed to overwhelm Ukrainian air defenses.

Both Moscow and Kyiv appear to be stepping up their attacks ahead of President-elect Donald J. Trump’s inauguration in January. Mr. Trump has said he wants to bring a swift end to the war in Ukraine but has not said how, leading to speculation over whether he will maintain the same level of robust military support provided to Ukraine under the Biden administration.

Mr. Zelensky has said he believes that the only way to force Moscow into peace negotiations is by showing strength and shoring up Ukraine’s position on the battlefield — with the help of its allies. He drove that point home again in an interview with Fox News that was broadcast Tuesday evening.

As long as Europe, the United States and the people of Ukraine remain united, he said, they could force President Vladimir V. Putin of Russia to accept a just and lasting peace.

“Putin is weaker than the United States of America,” Mr. Zelensky said. And Mr. Trump, he added, “is much stronger than Putin.”