Russia pummeled Ukraine’s second-largest city, Kharkiv, overnight on Saturday, using a swarm of drones, bombs and missiles that killed at least three people, according to the local authorities. It was the latest in an escalating series of Russian air assaults on urban centers that have further dampened hopes for a cease-fire.

Located just 20 miles from the Russian border, Kharkiv is a frequent target of Russian air assaults. What set the latest attack apart was the sheer volume of weapons launched in a short span of time.

The local authorities said that within 90 minutes, Russia struck the city with nearly 50 drones, two missiles and four glide bombs, powerful guided weapons that carry hundreds of pounds of explosives. Kharkiv’s mayor, Ihor Terekhov, said that 40 explosions were heard in the city. He described the overnight assault as “the most powerful attack” on the city since Russia’s full-scale invasion of Ukraine began more than three years ago.

Photos released by Ukraine’s emergency services showed the upper floors of a residential block ablaze, with white smoke pouring into the early morning sky. In other images, rescuers sifted through the charred wreckage of a gutted apartment. Parts of the photos were blurred, likely to hide the remains of two people killed in the strike, according to the rescuers.

A third person died elsewhere in Kharkiv, and about 20 others were injured in the assault.

The attack came as Russian forces about 100 miles north of Kharkiv pushed deeper into Ukraine’s northeastern Sumy region, seizing two more villages and advancing their effort to carve out a buffer zone along the Russia-Ukraine border.