Ukraine's acting president says the commander of the country's navy has been freed after being held by Russian forces and local Crimean militia at the navy's headquarters.

Rear Adm. Sergei Haiduk and an unspecified number of civilians were held for hours after the navy's base in Sevastopol was stormed Wednesday. Early reports said the storming was conducted by a self-described local defense force, but the statement by President Oleksandr Turchynov on Thursday said Russian forces were involved.

The statement said Haiduk and the civilians were released, but did not give details.

The storming came hours before Ukraine announced plans to withdraw troops from Crimea, which was formally annexed by Russia this week. The annexation is widely regarded abroad as illegitimate.