Friday morning, dozens of armed men in military uniforms without insignias surrounded two Crimean airports in what Ukraine's Interior Minister Arsen Avakov has declared an "invasion and occupation" by Russian forces. The incident comes one day after masked gunmen, believed to be pro-Russia militants, seized two government buildings in the region.

The soldiers have stationed themselves outside of airports in Simferpol, the region's capital, and Sevastopol. There's no sign they've entered any terminals, and flights are reportedly arriving and departing on schedule.

While Russia's Black Sea Fleet, which is stationed in Crimea, has denied any involvement in the incident, BBC reporters spotted eight Russian military personnel trucks heading towards Simferopol on Friday, and there have been multiple unconfirmed reports of eight Russian military helicopters in the area.

Oleksandr V. Turchynov, Ukraine's speaker of Parliament and its acting president, called a meeting on Friday of the National Security and Defense Council to discuss the situation in Crimea.

"Terrorists with automatic weapons, judged by our special services to be professional soldiers, tried to take control of the airport in Crimea," he said before the meeting, according to the New York Times.

His colleague, Ukraine's interior minister Aresen Avakov, described the incident in more detail on his Facebook page.

According to Avakov, at about 1:30 am Friday morning, several trucks carrying more than 100 troops entered the Simferopol airport with automatic weapons.

When Ukrainian security forces told the men—who Avakov said did not hide their affiliation to Russia— they did not have the right to be there and must leave, the men responded, "We do not have instructions to negotiate with you."

"Tension is building," Avakov wrote, adding: "I regard what is happening as an armed invasion and occupation in violation of all international treaties and norms. This is a direct provoking of armed bloodshed on the territory of a sovereign state."

Concerns about separatism and Russian intervention in Crimea, which, according to a 2001 census, is 58% ethnic Russian, have soared in Ukraine since last week's ousting of Ukrainian President Viktor Yanukovych and have slowed the process of establishing a new permanent government.

[Image via AP]