Ukraine on 'full combat alert' as president warns threat of Russian invasion 'is real'

Oleksandr Turchynov spoke of a possible invasion from 40,000 Russian troops gathered at the border with Ukraine

A pro-Russian activist walks in front of Ukrainian riot police during a rally in Donetsk (Reuters)

Ukraine is on “full combat alert” over a possible invasion by Russian troops gathered at the border as the interim president warned that “the threat of Russia starting a war against mainland Ukraine is real."

Oleksandr Turchynov made the remarks during a ministerial meeting, where he also told regional governors Ukraine’s police and security forces are "helpless" to quell unrest in two eastern regions bordering Russia.

In some cases they are even cooperating with pro-Russian militants who have seized scores of government buildings and taken people hostage, the interim president said today.

Mr Turchynov said the goal now was to prevent the agitation from spreading to other territories.

"I will be frank: today, security forces are unable to quickly take the situation in the Donetsk and Luhansk regions under control," Mr Turchynov told the meeting.

"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 organisations."

His comments came as pro-Russian separatists seized control of state buildings in the town of Horlivka, a city in the crisis-torn eastern Ukraine.

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The Horlivka's police headquarters had been stormed by pro-Russian militants earlier in April but separatists took over the police division in town and the government administration on Wednesday.

Eastern Ukraine, with a large Russian-speaking population, was the heartland of support for Viktor Yanukovych, the Russia-friendly president who was ousted in February.

Russia has deployed an estimated 40,000 troops to the border with Ukraine since March.

The Kremlin has always denied plans to build on last month’s annexation of Crimea with an invasion of eastern Ukraine, but has maintained the right to intervene with force if ethnic Russians come under threat.

Additional reporting by agencies