Ukraine says 13 of its servicemen have been killed and 20 wounded in the fighting with Russia-backed separatist forces over the past 24 hours.

Security Council spokesman Vladimir Polevoi said Sunday that the fiercest battles were still for control over Debaltseve, a government-held railway hub that the rebels need to further consolidate their control in eastern Ukraine.

The spokesman said the separatists were attacking several villages around Debaltseve.

An Associated Press journalist saw more than a dozen Ukrainian tanks and other heavy military vehicles, including a rocket launcher, heading toward Debaltseve on Sunday, apparently to reinforce the government troops.

A month of relative quiet in eastern Ukraine was shattered in early January by full-blown fighting as the separatists attempted to claw back additional territory from the government.