'Loud explosions' in Kyiv as Russia again strikes capital, US ambassador says

KYIV and LONDON -- Russia launched an attack on Kyiv and other Ukrainian cities early Tuesday, continuing its escalated large-scale attacks on residential areas, local officials said.

Air raid sirens in Kyiv began to sound just before 6 a.m. The attacks, which also hit Kharkiv, lasted about four hours, with Russia launching about a dozen ballistic missiles and about 35 Iranian-made drones, Ukrainian officials said.

At least five people were killed and 101 were injured in Tuesday's attacks, Ukrainian President Volodymyr Zelenskyy said.

"Putin is ringing in 2024 by launching missiles at Kyiv and around the country as millions of Ukrainians again take shelter in freezing temps," U.S. Ambassador Bridget A. Brink said on social media.

She added, "Loud explosions in Kyiv this morning. It's urgent and critical that we support Ukraine now -- to stop Putin here."

The Russian Defense Ministry said it was targeting Ukrainian missile and drone plants in Kyiv and its suburbs, as well as "depots storing missiles, ammunition and air-launched weapons supplied by the West."

"The strike achieved the objective. Every target was hit," the defense ministry said.

Russia's military had targeted civilian areas in Ukraine over the weekend, launching at least nine missiles and at least 49 drones before 6 a.m. Sunday.

Russian officials accused Ukraine of a strike on Saturday in Belgorod, Russia. That strike killed at least 21 people, according to the Russian Ministry of Emergency Situations. Ukraine has not claimed responsibility.

During a visit to a military hospital on Monday, Russian President Vladimir Putin called the Belgorod strike a "terror attack."

"Just a strike, a targeted strike on the civilian population," he said. "Of course, it is a terror attack, there is no other way to describe it."

ABC News' Joe Simonetti and Will Gretsky contributed to this report.