Russian troops forced their way into a Ukrainian marine base in the Crimean port city of Feodosia early this morning, overrunning one of the few symbols of resistance left after Moscow wrestled the peninsula away from Kiev, defending soldiers inside said.

The Russians used stun grenades and fired automatic weapons as they charged in, a Ukrainian military official said. Ukrainian flags were taken down from flagpoles inside the base.

Ukrainian army officer, First Lieutenant Anatoly Mozgovoy, told Reuters by phone from inside the compound that the Russians had fired shots and the Ukrainian soldiers were unarmed. Asked if the base had been taken over, he said: "Yes".

"The invading troops were using stun grenades and also firing automatic weapons. The interior of the compound is full of Russian troops," said Vladislav Seleznyov, a Ukrainian military spokesman in Crimea.

Russian forces had already captured part of the base, used by the 1st Separate Marine Battalion, Ukraine's top military unit, earlier this month.

But Ukrainians had previously appeared to be in control of the armoury, the barracks and other facilities in the compound.

Russia's seizure of Crimea, a Black Sea peninsula of two million people with a narrow ethnic Russian majority, has been largely bloodless.

Moscow formally annexed Crimea on Mar. 21 in a move not recognised by Kiev and the West, prompting sanctions on Russia over the Cold War-era style conflict.