Speaking to a ministerial meeting on Wednesday in Kyiv, interim President Turchynov said, "Our armed forces are on full combat alert," adding that "the threat of Russia starting a war against mainland Ukraine is real."

Ukraine's defense forces have been on high alert for several weeks as armed separatists have seized more than a dozen government buildings in eastern Ukraine despite an operation by Ukraine's army and police to oust the pro-Russian groups.

Most recently, armed insurgents took control of the city council building and police station in the city of Horlivka in the Donetsk region on Wednesday morning.

Turchynov told the cabinet meeting that "our number one task is to prevent terrorism spreading from the Donetsk and Luhansk regions to other Ukrainian regions."

The interim president also urged "Ukrainian patriots" to bolster the beleaguered police force who he said 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."

Russia has deployed tens of thousands of troops to its shared border with Ukraine. The move has been viewed by the international community as precursor to staging of a military intervention or annexation. The Black Sea peninsula of Crimea was annexed by Russia in March and Russian President Vladimir Putin asserts he has a "right" to send his forces into Ukraine but has not yet done so.

The West has accused Russia of fomenting the crisis and has imposed sanctions to try and get Moscow to back down ahead of Ukraine's upcoming presidential elections on May 25.

Eastern Ukraine is made up of a large Russian-speaking population and was the heartland of support for former president, Viktor Yanukovych, who was ousted and fled to Russia in February.

hc/mz (Reuters, AFP, AP, dpa)