By Will Stewart and David Williams and James Rush and Damien Gayle

The Ukraine crisis took a dramatic turn last night when Russian troops stormed a key command post in Crimea.

While no shots were fired, it is the first time the Russians have used force to increase their grip on the disputed peninsula.

The act of aggression took place in the strategic port of Sevastopol, home of Russia’s Black Sea fleet, which includes 24 warships, two submarines and 16,000 sailors and marines.

Tensions were already high yesterday when a U.S. warship arrived in the Black Sea. The arrival of the guided missile destroyer USS Truxtun was officially described as ‘routine’ by Washington.

But its presence was seen as hugely significant just hours after the Pentagon unveiled a large increase in air power in the region.

Last night Russian leader Vladimir Putin appeared relaxed as he officially opened the Winter Paralympic Games in the Black Sea resort of Sochi.

The president was centre stage once again as he was watched by hundreds of millions on TV at the games – which will still be attended by Ukraine athletes despite calls for their withdrawal.

Meanwhile, the US has been dispatching warplanes in an effort to reassure allies alarmed by Russia’s effective seizure of Ukraine’s Crimea peninsula. Six F-15 jets and one KC-135 refuelling aircraft were sent to join Nato patrols in the Baltics. A further dozen F-16 fighters will be deployed next week.

The increase in US military muscle in the region came as the Turkish Air Force scrambled six F-16 fighter jets after a Russian surveillance plane flew along its Black Sea coast. Georgia also sent up its warplanes this week.

Tensions continued to rise yesterday following a declaration from Ukraine that ‘no one in the civilised world’ would recognise a planned referendum by the Crimean parliament on joining Russia.

Mr Putin again rebuffed a warning from US President Barack Obama over Moscow’s military intervention in Crimea, insisting that the Kremlin could not ignore calls for help from Russian speakers in Ukraine.

After an hour-long telephone call, Mr Putin said Moscow and Washington were still far apart on the situation in the former Soviet republic, where he said the new authorities had taken ‘absolutely illegitimate decisions on the eastern, south eastern and Crimea regions’.

‘Russia cannot ignore calls for help and it acts accordingly, in full compliance with international law,’ he said.