European Union and G7 leaders meet during the Nuclear Security Summit in The Hague on Monday - from left to right, European Council President Herman Van Rompuy, Canadian Prime Minister Stephen Harper, French President Francois Hollande, British Prime Minister David Cameron, US President Barack Obama, German Chancellor Angela Merkel, Japanese Prime Minister Shinzo Abe, Italian Prime Minister Matteo Renzi and European Commission President Jose Manuel Barroso. Jerry Lampen / Reuters

As the United States redoubled efforts to put pressure on Russia for its takeover of Crimea, Moscow shrugged off US President Barack Obama's drive to isolate Russian President Vladimir Putin's government.

The US and some of its closest allies cut Russia out indefinitely from a major coalition of leading industrial nations and canceled a summer summit that Russia was to host in its Olympic village of Sochi.

Obama also sought to win backing from other foreign leaders in hopes of ostracizing or even shaming Putin into reversing his acquisition of Crimea and backing away from any designs he might have on other Eastern European territory, The Associated Press reported.

In a strongly worded joint statement, the United States, France, Canada, the United Kingdom, Germany, Italy and Japan denounced a referendum in Crimea to secede from Ukraine and Russia's ensuing takeover. In so doing, the seven leaders also excluded Russia from what had been a two-decade-old coalition known as G8.

Meanwhile, Russian presidential spokesperson Dmitry Peskov told ITAR-Tass that the Kremlin believes the unwillingness of the G8 member countries to continue cooperation with Russia on the G8 agenda is counterproductive.

"As for the contacts with the G8 countries, we are ready for them, we are interested in them, but the unwillingness of other countries to continue the dialogue, in our view, is counterproductive both for us and our partners," he said.

The G7 leaders claim that "this group came together because of shared beliefs and shared responsibilities" but "Russia's actions in recent weeks" (support for the Crimean referendum) allegedly are not consistent with them, according to ITAR-Tass.

"This clear violation of international law is a serious challenge to the rule of law around the world and should be a concern for all nations," the G7 declaration said.

Downplaying G8

Russia is not clinging to the G8 format, as all major world problems can be discussed at other international venues such as G20, Russia Today quoted Russian Foreign Minister Sergey Lavrov as saying.

"The G8 is an informal club, no one gives out membership cards and no one can expel members," Lavrov said. "If our Western partners believe that this format has exhausted itself, let it be. We are not clinging to it."

He added that many believe that the G8 has already fulfilled its mission as many issues are now discussed at the G20 forum.

"Generally speaking, there are also other formats for considering many questions, including the UN Security Council, the Middle East Quartet and the P5+1 on the Iranian nuclear problem," Lavrov said.

The minister also commented on earlier reports regarding Australia considering not inviting Putin to the November G20 meeting, to be held in Brisbane.

"The G20 was not established by Australia, which voiced the proposal not to invite Russia to the meeting. We created the format all together," Lavrov said.

It will be the first time since Russia joined G8 in 1998 that it will have been shut out of the annual summit of industrialized economies.

The United States and the European Union have imposed some sanctions on Moscow, including visa bans for some of Putin's inner circle, and warned of additional measures if Putin does not change course.

In the Crimean Peninsula, Ukraine ordered its troops to pull back from the disputed territory, a clear signal that at least for now the fledgling Ukrainian government in Kiev was ceding to Russia's tactics, the AP reported.

Ukraine has so far dominated Obama's side discussions with world leaders and the G7 members. Even Lavrov, in The Hague for the nuclear summit, met on the sidelines with US Secretary of State John Kerry.

AP - Reuters