Russia said Tuesday it was quitting the Council of the Baltic Sea States amid raging tensions with the West over Moscow's offensive in Ukraine.
The organisation is a political forum for regional cooperation that groups together 11 member states such as Germany, Finland and Norway as well as the European Union.
The foreign ministry in Moscow said that the organisation was becoming "an instrument of anti-Russian policy" and "increasingly mired in Russophobia and lies."
"We consider our country's further presence in the CBSS to be inexpedient and counterproductive," the foreign ministry said in a statement.
Moscow said the organisation planned to hold a meeting in Norway on May 25 without Russia's participation, accusing the group of stealing the country's contribution to its budget.
Despite leaving the council, Moscow said it would remain present in the Baltic region.
"Attempts to oust our country from the Baltics are doomed to failure," the ministry said.
Separately, Moscow also said on Tuesday that two employees of Finland's embassy in Russia would have to leave the country in response to a similar move by Helsinki.
The foreign ministry said in a statement that it summoned Finland's ambassador to Moscow and expressed its "strong protest" against the expulsion of two Russian diplomats from Finland in April.
Moscow also accused Finland of taking a "confrontational course" towards Russia, supplying weapons to Ukraine and "covering up the crimes of Ukrainian nationalists" against civilians.
"The Russian side made a decision on the unacceptability of the further stay in the Russian Federation of two staff members of Finland's embassy in Moscow," the ministry said. Since President Vladimir Putin sent troops to
Ukraine on February 24, the West has expelled dozens of Russian diplomats and Russia has retaliated in tit-for-tat moves.
Finland shares a 1,340-kilometre (830-mile) land border with Russia and recently confirmed its intention to join NATO after decades of military non-alignment.