By Alissa de Carbonnel
BALAKLAVA, Ukraine, Feb 28 (Reuters) - At least 20 men wearing the uniform of Russia's Black Sea fleet and carrying automatic rifles surrounded a Ukrainian border guard post on Friday, in a tense standoff near the port city of Sevastopol in Ukraine's Crimea region.
A Reuters reporter in the Balaklava district 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."
He was referring to Kiev's Independence Square, the cradle of a popular uprising that ousted President Viktor Yanukovich.
The servicemen's presence appeared to confirm the veracity of a statement by the Ukrainian border guard service that Russian servicemen were blocking off a unit of Ukrainian border guards in Balaklava.
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 earlier on Friday.
Russia says it has not violated an agreement on the movement of its military in Crimea.
Yanukovich appeared at a news conference in Russia on Friday but did not seek Russian military intervention in Ukraine following his ouster last Saturday.
"I think any military action in this situation is unacceptable," he said. "I have no plan to ask for military support."
He said Crimea, the only region in Ukraine with an ethnic Russian majority, should remain part of the country.
Some ethnic Russians want Russia to reclaim Crimea, gifted to then Soviet Ukraine in 1954 by Soviet Communist leader Nikita Khrushchev.