Armed men stand guard at the Simferopol airport in the Crimea regio. Picture: Baz Ratner

London - Britain is advising against all travel to Ukraine's Crimean Peninsula and telling its citizens now there to leave.

The situation on the strategic peninsula has become tense as masked gunmen have taken control of government buildings, airports, and other strategic sites in the wake of a three-month protest which saw pro-Russian President Viktor Yanukovych pushed from power.

Ukraine has accused the Kremlin of invading Crimea, saying Russian troops have taken up positions around a coast guard base and two airports.

Britain's Foreign Office said Friday that it advised British nationals to avoid Simferopol's airport, where gunmen in unmarked military uniforms were patrolling with assault rifles.

On Thursday Czech Foreign Minister Lubomir Zaoralek said he and fellow diplomats would not travel to Crimea while in Ukraine because of security concerns.