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.

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.

Romanian prosecutors detained six people on charges of forming an organised criminal group and treason, they said on Thursday, adding that members of the group repeatedly contacted agents of a foreign power both in Romania and in Russia.

Romania on Wednesday ordered two Russian diplomats expelled, after slamming Russian "interference" and criticism of an indictment of far-right presidential candidate Calin Georgescu. Russia's military attache and his deputy in Bucharest were declared "persona non grata" by Foreign Ministry of Romania,