Three explosions were heard, then electricity was cut out on Tuesday in Ukraine's second city of Kharkiv, a Reuters witness reported.
"There are no lights in some parts of the city. Information about casualties is being specified," Kharkiv's mayor, Ihor Terekhov, said on his Telegram channel. He also reported a fourth attack.
Terekhov said an infrastructure facility was hit and said authorities were working to restore power as quickly as possible.
The report followed a rocket attack on Kharkiv on Sept. 9 in which at least 10 people were wounded. Ukrainian officials said that attack was revenge for its forces' successes on the battlefield against Russia.