Crimea's regional parliament has declared independence from Ukraine ahead of a referendum on whether voters want to secede from Kiev rule.

The document, approved by 78 out of 100 assembly members, specifies that Crimea will become an independent state if its residents vote in favour of joining Russia in the referendum.

Ukraine's interim government has called the 16 March referendum illegal, as have the US and EU.

Pro-Russian volunteer soldiers swore an oath of allegiance in the semi-autonomous region in front of prime minister Sergei Aksyonov. The 36 volunteers pledged to "defend the people of Crimea".

"You are now part of the bulwark defending the people of Crimea," Aksyonov, a shadowy businessman with a murky past nicknamed "The Goblin", said.

Tensions in Crimea, the only region of Ukraine populated by an ethnic Russian majority, have been rising after rebel protesters ousted Kremlin-backed president Viktor Yanukovich.

The region has been taken over by armed troops said to be Russian soldiers. Alongside them, self-defence groups and Cossacks have been patrolling key locations in the peninsula.

A leader of Crimea's Muslim Tatars said that occupying Russian forces would face bloody reprisals if the referendum were successful.