Ukraine refuses to follow "a scenario written by the Kremlin" but will not intervene militarily in Crimea, acting president Oleksander Turchynov has told the AFP news agency.

With the strategic Black Sea peninsula threatening to secede from Ukraine, Turchynov said Kiev would not launch a military operation in the southeastern region, where Russian-backed forces have seized de facto control, because it would risk exposing its eastern border.

The acting president, who came to power last month after violent protests brought down the previous pro-Moscow government, also condemned a forthcoming referendum in Crimea as a "sham", the results of which will be fixed in Moscow.

"We cannot launch a military operation in Crimea, as we would expose the eastern border (close to Russia) and Ukraine would not be protected," Turchynov said as the worst East-West crisis since the Cold War continued to escalate.

The tensions in Crimea have led to mass protests in parts of southern and eastern Ukraine – mostly Russian-speaking regions – with protesters storming the regional government buildings in the cities of Donetsk and Lugansk.

While Turchynov shied away from going on the offensive in Crimea, Turchynov insisted Ukraine would "not be inactive in the face of continued aggression".

"They (Russia) can attack our military units in Crimea, spread their aggression on the continent. The army will react," he vowed.

Crimea is due to hold a referendum Sunday on joining Russia, and on Tuesday, the pro-Moscow authorities in the autonomous Black Sea peninsula took the additional step of voting for full independence from Ukraine.

"The Russian forces don't intend to hold a referendum, they're just going to falsify the results," he added, saying "no civilised country will recognise these results."