Russian soldiers 'surround Ukraine border guard base'

At least 20 men wearing the uniform of Russia's Black Sea fleet and carrying automatic rifles surrounded a Ukrainian border guard post in a tense standoff near the port city of Sevastopol in Ukraine's Crimea region.

A Reuters reporter saw Ukrainian border police in helmets and riot gear shut inside the border post, with a metal gate pulled shut and metal riot shields placed behind the windows as protection.

A servicemen who identified himself as an officer of the Black Sea Fleet told Reuters: "We are here ... so as not to have a repeat of the Maidan."

Maidan is Kiev's Independence Square, the cradle of a popular uprising that ousted President Viktor Yanukovich.

The servicemen's presence appeared to confirm an earlier statement by the Ukrainian border guard service that Russian servicemen were blocking off a unit of Ukrainian border guards.

Russia's Black Sea fleet has a base in Sevastopol but Moscow denies its forces have been involved in the rapidly changing events in Crimea, where armed men took control of two airports.

Russia says it has not violated an agreement on the movement of its military in Crimea.