Russia unleashed a drone and missile strike on the southeastern Ukrainian city of Zaporizhzhia overnight, killing one, wounding 31 others and leaving tens of thousands without power or heat, officials said on Thursday.

Ukraine has intensified missile and drone strikes on Russia. Russian air defenses are stretched, prompting efforts to find other approaches to protect domestic targets.

Ukrainian authorities issued air raid alerts for the entire country on Saturday, as the air force warned of missile and drone threats in multiple regions. "Missile threat to Mykolaiv and Kherson regions," the air force said on Telegram, adding that missiles were moving toward the Sumy and Poltava regions as well.

The drone blew out a wall and surrounding windows in the building in Sumy, a major city, just after 1 a.m., the Sumy regional administration said.

"This refinery is one of the 10 largest oil refineries in Russia in terms of design capacity and is involved in supplying the Russian occupatying army," the General Staff said in a statement.

A Russian drone attack on a residential block killed eight people including three elderly couples in the eastern Ukrainian city of Sumy, prosecutors said on Thursday.

Ukrainian soldiers are now using a long-range drone capable of traveling up to 2,000 kilometers (1,242 miles) and carrying a 250-kilogram air bomb, the Unmanned Systems Forces said on Jan. 31. The drone is described as a “unique development” and a potential game changer on the battlefield.