Russian troops have surrounded a Ukrainian airbase in Crimea and issued an ultimatum to forces inside to surrender, the deputy commander of the base in Belbek, near Sevastopol, said on Saturday.

The base, above which the blue and yellow Ukrainian flag was flying, is one of the few military facilities on Crimea still controlled by Ukraine after the annexation of the peninsula by Russian forces.

"The Russian troops at our aerodrome gave us an hour to surrender or they will start storming. We are going nowhere, let's see what this storming is," Oleg Podovalov told Reuters.

The ultimatum was due to expire at 0730 am ET, but there was no sign of the Russians moving in on the base.

The Russian takeover of the Black Sea peninsula has been largely bloodless, though one Ukrainian serviceman was killed and two others wounded in a shooting in Simferopol earlier this week.

Ukraine's Defence Ministry said on Friday Crimea's bases were still formally under Ukrainian control, but most are now occupied by Russian troops and fly Russia's tricolor flag.-Reuters