Ukraine and Russia traded blame for a deadly missile strike on Saturday that killed at least four people in the dormitory of a boarding school situated in a part of Russia's Kursk region held by Kyiv forces.

Some of the war's fiercest battles in recent months have been taking place in the Kursk region that borders Ukraine, where Kyiv forces have held swathes of the land since staging a major cross-border incursion last August.

Ukraine's Armed Forces said on the Telegram messaging app that Russia had launched an aerial bomb from Russian territory that struck a boarding school in Sudzha, killing at least four. The boarding school housed people preparing for evacuation.

As of 10 p.m. (2000 GMT) on Saturday, 84 people had been rescued or received medical assistance, the statement said. Four of the injured were in a serious condition. Rescue efforts to clear rubble were proceeding.

Ukrainian President Volodymyr Zelenskiy said the attack on Sudzha, some 12 km (7.5 miles) from the border with Ukraine, showed how Russia fights the war.

"They destroyed the building even though dozens of civilians were there," Zelenskiy wrote on the X social media platform.

"This is how Russia waged war against Chechnya decades ago. They killed Syrians the same way. Russian bombs destroy Ukrainian homes the same way."

Russia's Defence Ministry said early on Sunday on Telegram that Ukrainian forces had launched "a targeted missile strike on a boarding school in the city of Sudzha" from Ukrainian territory.

In a statement, Russian foreign ministry spokesperson Maria Zakharova called the strike a "terrorist attack" and vowed to bring Kyiv to justice.

Russia's acting governor of the Kursk region, Alexander Khinshtein, also blamed Kyiv forces for the strike and said there was no reliable information yet about the number of potential victims.

Ukraine's military spokesperson, Oleksiy Dmytrashkivskyi, had earlier said in a video posted on Facebook that nearly 100 people were under rubble at the site, which he said had housed mostly elderly and infirm people.

Reuters was not able to verify the claims by either side independently, and the scope of the attack remained unclear.

Both sides deny targeting civilians in the war that Russia launched with its full-scale invasion in February 2022. Thousands of civilians, however, have been killed, the vast majority of them Ukrainian.