SIMFEROPOL, Ukraine (REUTERS) - A Ukrainian officer was wounded in a shooting at a military facility on the outskirts of the Crimean capital Simferopol on Tuesday, a military spokesman said, but it was unclear who was behind the incident.

"An officer was wounded in the neck," said Vladislav Seleznyov, a Ukrainian military spokesman in Crimea.

Some Ukrainian military facilities in Crimea have been under the control of Russian forces for several weeks after Russian troops poured into the Black Sea peninsula ahead of a referendum at the weekend that handed over control from Ukraine to Russia.

There was no immediate evidence that Russian soldiers were involved in Tuesday's incident, witnesses said.

It was not possible to see far into the compound, because streets leading to it had been blocked by so-called"self-defence" units of pro-Russian volunteers who have been patrolling the streets of Crimea in the runup to the referendum.

There have been major concerns over whether the governments of Russia and Ukraine, who are at loggerheads over Moscow's annexation of Crimea, could achieve a smooth handover of control of Ukrainian military bases in the region.

Pro-Russian nationalists have been seen gathering outside Ukrainian military bases on several occasions this month, demanding that Ukrainian soldiers leave and hand over control to Russian forces.

The fact that the road blocks outside the facility in Simferopol were staffed by "self-defence" units suggested it was they who were involved in the incident rather than Russian forces. The situation was calm by 1520 GMT.

On Sunday, the Ukrainian and Russian Defence Ministries said they had agreed on a truce.