The mayor of Ukraine's capital city of Kyiv Vitali Klitchko said on Friday five blasts were heard in a close interval of three to five minutes near a power station in the north of the city.

"The emergency services are underway. We're finding out the details," he said.

He added that bridges in the city had been taken under protection and special control, as Russian troops are nearing, while checkpoints are being installed near strategic city objects.

"The situation now - without exaggeration - is threatening for Kyiv. The night, close to the morning, will be very difficult".