Ukraine said military operations against pro-Russian separatists in the industrial east of the country continued at dawn on Saturday near the town of Kramatorsk, vowing it would not stop a bid to dislodge them.

Interior Minister Arsen Avakov said Ukrainian forces had seized control of a television tower in Kramatorsk, near the rebel stronghold of Slaviansk, but gave no information on possible casualties.

Slaviansk was the target on Friday of the most significant advance by Ukrainian forces since the start of an armed uprising in the east a month ago, stalled by well-armed separatists who brought down two military helicopters and dug in in the town of 130,000.

"The active phase of the operation continued at dawn," Avakov wrote on his Facebook page. "We are not stopping."

Overnight, Russian media reported fighting near Kramatorsk, citing hospital sources as saying one person had been killed and nine wounded.

That followed the deaths of two helicopter crew in Slaviansk. Separatists said three fighters and two civilians were also killed in the Ukrainian advance on the town.

The toll, however, was eclipsed by the deaths of dozens of people in a fire and street-fighting between pro- and anti-Russian groups in Odessa on Ukraine's Black Sea coast on Friday, opening a new front in a conflict that has split the country.

Regional police in Odessa put the death toll at 37, most of whom were killed when the trade union building in the city was set on fire. It said 200 people had been wounded. Local authorities had previously said 43 people had died.