The Russian-battered eastern Ukrainian city of Sievierodonetsk appeared to be on the brink of becoming another Mariupol on Monday as the mayor told The Associated Press that Russian troops have entered, power and communications have been cut and “the city has been completely ruined.”

Moscow seeks to capture all of Ukraine’s industrial Donbas region, and Sievierodonetsk is key to that. Fierce street fighting is underway in the city as Ukrainian defenders are trying to push the Russians out, Mayor Oleksandr Striuk told the AP in a phone interview. Russian troops have advanced a few blocks toward the city center, he said.

“The number of victims is rising every hour, but we are unable to count the dead and the wounded amid the street fighting,” the mayor added. He said 12,000-13,000 civilians left in the city that once held more than 100,000 are sheltering in basements and bunkers to escape the Russian bombardment.