Russian military forces have occupied an airport in the Black Sea port of Sevastopol in Crimea near the Russian naval base in an "armed invasion", Ukraine's interior minister has said.
On a day of escalating tensions between the two countries, eight Russian military helicopters were also reportedly seen flying towards the Belbek international airport in Sevastopol, although a video purporting to show the aircrafts landing has not been verified.
Another airport, Simferopol, has also been occupied by armed men, also thought to be pro-Russia militia. Eight army trucks with Russian plates were also moving towards Simferopol, the BBC has reported.
Ukraine's State Border Guard Service said about 30 Russian marines had taken positions outside its Coast Guard base in the Sevastopol base. The interior minister, Arsen Avakov said: "I consider what has happened to be a military invasion and occupation in violation of all international agreements and norms."
In response, Russia's Black Sea Fleet has denied its forces were involved in a seizure or blockade of the airport, according to the Interfax news agency.
"No units of the Black Sea fleet were deployed in the area of Belbek nor did they take place in blockading it," a statement from the fleet's press service said.
In other developments today, France, Germany and Poland released a joint statement saying they are "very worried" by the events and urged all parties to refrain from any action endangering Ukraine's territorial integrity.
Meanwhile, Ukraine's acting president Olexander Turchynov signed a decree dismissing the head of the armed forces general staff, his office said on Friday. Admiral Yuriy Ilyin was only appointed at height of protests against the ousted president Viktor Yanokovych.
The Ukrainian parliament has asked the UN Security Council to discuss the escalating situation in Crimea and Mr Turchynov has called an emergency session of security chiefs to discuss the situation in Crimea.
He proposed parliament hold a vote to adopt an appeal to Russia to "respect Ukraine's territorial integrity" and "reject support for separatism in Ukraine, of any form".
But what really happen...
But what really happen...
Crimean leader claims control, asks Putin for help
The pro-Russian prime minister of Ukraine's restive Crimea claimed control of all military, police and other security services in the region Saturday and appealed to Russia's president for help in keeping peace there. President Obama warned Moscow "there will be costs" if it intervenes militarily.
In a statement reported by local and Russian news agencies, Sergei Aksenov declared that the armed forces, the police, the national security service and border guards will answer only to his orders. He said any commanders who don't agree should leave their posts.
As armed men described as Russian troops took control of key airports and a communications center in Crimea on Friday, Ukraine accused Russia of a "military invasion and occupation" — a claim that brought an alarming new dimension to the crisis, and raised fears that Moscow is moving to annex a strategic peninsula where Russia's Black Sea fleet is based.