Ukraine plunged deeper into crisis yesterday as the country was caught in the middle of a power struggle between Western powers and Russia.

Russian forces coasted into the Crimean peninsular over the weekend without firing a shot after President Vladimir Putin persuaded the Duma to authorise military action.

Thousands marched through Moscow yesterday in support of a full-fledged invasion, wanting to claim back the majority Russian Crimea, which was transferred to Kiev in 1954.

Ukrainian coup president Oleksandr Turchynov ordered troops to full combat readiness on Saturday and called up army reservists in response to Russia’s actions, but so far the thinly supported government has been powerless to resist Moscow.

Muscovite mouthpiece Russia Today claimed that Ukrainian troops in the Crimea had deserted en masse.

“A number have been disarmed, while another big portion is switching to the Crimean side,” regional deputy PM Rustam Temirgaliev reportedly said.

But unidentified troops were engaged in a standoff outside a Crimean military base at Perevalne late yesterday.

A dozen soldiers with a tank faced off against a convoy of around four armoured vehicles and 13 trucks with Russian plates, each carrying around 30 soldiers.

The head of Ukraine’s navy — who was only appointed to the post on Saturday — defected yesterday.

Rear Admiral Denis Berezovsky pledged to “strictly obey the orders of the supreme commander of the autonomous republic of Crimea,” telling his forces to disregard orders from the “self-proclaimed” Kiev government.

US Secretary of State John Kerry blasted Russia’s “incredible act of aggression,” while Mr Putin defended his country’s right to protect its interests in the autonomous region.

Mr Kerry warned that Russia could be kicked out of the G8 and pledged the economic group’s June summit would not go ahead in Sochi as planned. Britain, France and Canada have also suspended their G8 preparations.

“You just don’t in the 21st century behave in 19th-century fashion by invading another country on a completely trumped-up pretext,” Mr Kerry said.

Nato secretary-general Anders Fogh Rasmussen said Russia’s actions threatened “peace and security in Europe,” adding that Ukraine was a “valued partner” of the imperialist bloc.

Nato was locked in discussions over the Ukraine as the Star went to press.