Russia has reiterated that its Black Sea Fleet will abide by international regulations but insisted the country's interests will be protected in Ukraine, even though Crimea's main airport of Simferopol is said to have been seized by dozens of unidentified armed men.

A day after Ukraine's interim president Oleksandr Turchinov said any unauthorised movement of Russian troops will be considered as "military aggression", Russia's foreign ministry responded: "Regarding the statements about Russia's violation of the agreements on the Black Sea fleet, we declare that in the current difficult situation the Russian Black Sea fleet is strictly adhering to said agreements."

Local reports said the Russian fleet's armoured units have already been dispatched, which does not require prior approval.

"Currently all units are engaged in their daily routines, including combat training," Russia's deputy defence minister Anatoly Antonov told reporters. He emphasised: "These actions do not represent a threat."

The strength and quality of weapons with the military personnel do not violate any of the existing bilateral agreements with Ukraine, he said.

Russia is also planning to send financial and humanitarian aid to Crimea. "Taking into consideration the official request of the authorities of Crimea regarding the financial aid, Russian President entrusted the Russian government to work on this issue with the regions of the Russian Federation," President Vladimir Putin's spokesperson Dmitry Peskov said.

The Russian statements have come alongside reports that nearly 50 armed men, carrying Russian flags, have taken control of the main airport in the Crimean capital.

Despite the presence of pro-Russian armed personnel, the airport is said to be operating normally and there is no disruption as yet, reports AFP.

"We are against fascism and nationalism. We are remaining outside the airport," a young lawyer, who identified himself only by his first name, Dmitry, said.

The reported siege came a day after the Crimean parliament was stormed by pro-Russian armed men leading to a call for referendum in the parliament over its secession from Ukraine.

This evoked a sharp response from Ukraine's interim head of state, who said: "Any movement, particularly with weapons, outside official residences regulated by our agreement will be interpreted by us as military aggression."

The acting president stressed the Ukrainian troops and police forces have been ordered to take "all measures" to protect Ukrainians.

Meanwhile, both the UK and the US have urged Russia to respect the territorial integrity of Ukraine and urged restraint.