Russian military forces are blockading Sevastopol airport in the Ukrainian region of Crimea, Ukraine's interior minister has said.

Arsen Avakov called their presence an "armed invasion", reports BBC.

Armed men also took over the other main Crimean airport, Simferopol, on Friday morning.

Witnesses told Interfax-Ukraine news agency that around 50 men arrived at Simferopol airport carrying Russian navy flags.

According to CNN, reports conflicted on whether they had taken control of the facility.

"We are checking to make sure that no radicals come to Crimea from Kiev, from the Ukraine," said one man, who didn't give his name.

"We don't want radicals, we don't want fascism, we don't want problems."

The airport is said to be operating as normal, says BBC.

A man called Vladimir told Reuters he was a volunteer helping the group, though he said he did not know where they came from.

"I'm with the People's Militia of Crimea. We're simple people, volunteers," he said.

"We're here at the airport to maintain order. We'll meet the planes with a nice smile - the airport is working as normal."