Romanian police say six people have been detained for allegedly organizing a criminal group that colluded with Russia to plot a coup against the government.

In an unprecedented move, authorities in Bucharest arrested six citizens Wednesday for organising a paramilitary group with Moscow's support, linked to the expulsion of the Russian military attache to Romania and his deputy.

Romanian prosecutors said on Thursday they had detained six people on charges of trying to overthrow the state with the help of Russia, marking a dramatic escalation of tensions between Bucharest and Moscow.