Crimea's pro-Russian authorities sought to boost their claim to break from Ukraine Monday as volunteer soldiers swore an oath of allegiance in front of prime minister Sergei Aksyonov.

Clutching Kalashnikov rifles to their chests and wearing fur-lined military fatigues, the 36 volunteers took their turns pledging to "defend the people of Crimea".

Before a large crowd of assembled journalists, Aksyonov, wearing a bullet-proof vest under his jacket and protected by two bodyguards, thanked the volunteers for their "devotion in this difficult time".

"You are now part of the bulwark defending the people of Crimea," he said.

He told journalists 186 volunteers had so far joined the new Crimean "self-defence" units after pro-Moscow forces took power in the region and announced their intention to join with Russia, with a referendum planned for Sunday.

"We have no intention of going to war with anyone," Aksyonov said. "We simply want to freely decide our own destiny. That is why we created armed forces. After the referendum they can be integrated into the Russian army."

Aksyonov said the Ukrainian soldiers who remain in Crimea, most of them inside bases surrounded by Russian troops, can join with pro-Russian forces or leave.

"After the referendum they will have to leave... or those who are citizens and who want to could swear allegiance to the autonomous republic of Crimea or the Russian Federation."