KYIV, Ukraine (AP) — A missile strike on a mail depot in the eastern Ukrainian city of Kharkiv killed six people, Ukrainian officials said Sunday.

A further 16 people were injured in the blast late Saturday, which is believed to have been caused by a Russian S-300 rocket, Kharkiv governor Oleh Syniehubov said on social media.

All of the victims were employees of private Ukrainian postal and courier service Nova Poshta.

In a statement, the company said that the air raid siren had sounded just moments before the attack, leaving those inside the depot with no time to reach shelter. It announced that Sunday would be a day of mourning for the firm.

Ukrainian President Volodymyr Zelenskyy described the strike as an attack on an “ordinary civilian object.”

“We need to respond to Russian terror every day with results on the front line. And, even more so, we need to strengthen global unity in order to fight against this terror,” he wrote on social media. “Russia will not be able to achieve anything through terror and murder. The end result for all terrorists is the same: the need to face responsibility for what they have done.”

Elsewhere in the Kharkiv region, three people were injured in Russian shelling on the city of Kupiansk, Syniehubov said.

The Ukrainian-held front-line city has been at the heart of fierce fighting as both Moscow and Kyiv push for battlefield breakthroughs amid the looming onset of wintry conditions.

Officials in southern Ukraine said Sunday that the Russian military had used a record number of aerial bombs over the country’s Kherson region in the past 24 hours.

Natalia Humeniuk, a spokesperson for the Ukrainian military’s Operational Command South, said that 36 missiles had been recorded over the area, with some villages being hit by several strikes.

___

Follow AP’s coverage of the war in Ukraine: https://apnews.com/hub/russia-ukraine