Ukrainian officials said on Thursday that at least 33 people were killed in a Russian airstrike on the city of Kramatorsk in the east of the country. These officials described the attack as a deliberate act against civilians, targeting one of the most important cities under Ukrainian control in the Donetsk region.

In the attack, which is considered one of Russia’s deadliest strikes this year, 18 other people were also injured. Ukraine’s police said the attack took place on a street where two city buses were traveling at the time of the bombing. Volodymyr Zelensky, the President of Ukraine, said the site of the strike was a bus station.

Reuters wrote that, according to local officials, Russian forces have increased drone attacks and bombing with guided bombs against Kramatorsk and other cities located in Ukraine’s defense belt. These cities are considered a main pillar of Ukraine’s defensive lines in the Donetsk region.