The commander of a surrounded Ukrainian military base in Crimea made a desperate appeal to his superiors Thursday to give him orders or he might have to shoot.

Yuliy Mamchur, commanding officer at Belbek air base in Crimea's capital Sevastopol, made his cry for help in a video address, broadcast on Ukrainian television, as tensions remained high on the Black Sea peninsula, now under de facto control by Russian forces.

"To avoid armed confrontations, I ask you to tell us as quickly as possible what commanding officers need to do if troops or members of their families come under threat," he urged.

"If you do not make a decision, we will act according to the status of the Ukrainian armed forces, even opening fire if need be," he warned.

Mamchur's appeal came as Russian forces have surrounded Crimean military bases for over a week and as the peninsula prepares to vote in a referendum on Sunday on joining Russia.

"We realise that we cannot resist for long against Russian troops that are greater in number, better armed and better trained, but we are prepared to fulfil our duty to the end," Mamchur said, adding that "Russian ultimatums have become increasingly demanding".

The defence ministry said interim Minister Igor Tenyukh had spoken to Mamchur on the phone Thursday, assuring him that "urgent measures" had been taken to back the units stationed in Crimea.

It did not however say what these measures were.