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Ukraine's armed forces are on full combat alert due to the "real danger" that war will break out with Russia, Kiev's acting president said Wednesday.

Oleksandr Turchynov added that his security forces were "helpless" to control unrest in the east of the country, where armed separatists are protesting against the Kiev government and agitating to join Russia.

"I am once again addressing the real danger of the start of a continental war against Ukraine by the Russian Federation," Interfax Ukraine quoted Turchynov as telling a meeting of regional leaders. "Our armed forces have been put on full combat alert."

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Pro-Russian groups have for weeks been occupying government buildings across the east, demanding a referendum similar to the one held in Crimea last month.

The city of Luhansk saw several more government offices seized Tuesday, and Horlivka, in the separatist-controlled Donetsk region, had its city council building and police station overrun on Wednesday.

Hours later, Turchynov told the meeting his forces were powerless to stop the uprisings.

"I will be frank: Today, security forces are unable to quickly take the situation in the Donetsk and Luhansk regions under control," Turchynov told the meeting, according to The Associated Press.

"The security bodies...are unable to carry out their duties of protecting citizens. They are helpless in those matters. Moreover, some of those units are either helping or cooperating with terrorist organizations."

Turchynov instructed the regional governors at the meeting to try to prevent the threat from overtaking more central and southern regions.

The Associated Press contributed to this report.