Escalating tension over Russia's annexation of Crimea, seven Western powers ousted Moscow from the G-8 and moved to shift the group's planned June summit in Sochi to a G7 meeting in Brussels.
The move to suspend Russia's membership in the G8 came at a meeting of the seven other leading industrialised nations on the sidelines of the Nuclear Security Summit at The Hague, according to a White House announcement.
"International law prohibits the acquisition of part or all of another state's territory through coercion or force," said a joint statement by US President Barack Obama and leaders of Canada, France, Germany, Italy, Japan and Britain.
"To do so violates the principles upon which the international system is built. We condemn the illegal referendum held in Crimea in violation of Ukraine's constitution.
"We also strongly condemn Russia's illegal attempt to annex Crimea in contravention of international law and specific international obligations," it said.
Reporting from The Hague, CNN cited Russian Foreign Minister Sergey Lavrov as saying earlier in the day that being kicked out of G8 would be no big deal.
"G8 is an informal organisation that does not give out any membership cards and, by its definition, cannot remove anyone," he was quoted as saying at a news conference.
"All the economic and financial questions are decided in G20, and G8 has the purpose of existence as the forum of dialogue between the leading Western countries and Russia."
Lavrov added that Russia was "not attached to this format and we don't see a great misfortune if it will not gather. Maybe, for a year or two, it will be an experiment for us to see how we live without it".
According to the Washington Post, at a meeting in The Hague Monday night, Russia also rallied support among the BRICS countries - Brazil, Russia, India, China and South Africa - with a denunciation of sanctions.
Russia, according to the Post report, said it expects to participate in the next meeting of the Group of 20 summit in Australia in November, despite warnings that it may not be welcome.
The BRICS statement argued that the host nation of a G-20 summit does not have the right to deny or suspend access to other members.
The Post also cited Australian Foreign Minister Julie Bishop as raising the possibility that Russian President Vladimir Putin might be barred from the summit.
Earlier Monday, Obama met Chinese President Xi Jinping to discuss a wide range of issues including Ukraine, Time reported.
But US Deputy National Security Adviser for Strategic Communications Ben Rhodes, according to Time, indicated that China will not support international sanctions efforts.
The G-8 traces its roots to the G-6 organised by France in 1975, becoming the G-7 with the addition of Canada. Russia was first invited to join in 1998.