The leaders of some of the world's leading industrialised nations have effectively suspended Russia from their group in a sign of Moscow's increasing isolation over its actions in Ukraine.
Prime Minister David Cameron, US president Barack Obama and the leaders of the other G7 countries took the step as the administration in Kiev ordered its troops to withdraw from Crimea, which has been annexed by Russia.
Instead of the planned G8 summit in Sochi in June, there will be a G7 meeting in Brussels.
In a statement issued following a hastily arranged meeting in The Hague, the G7 leaders said: " This group came together because of shared beliefs and shared responsibilities. Russia's actions in recent weeks are not consistent with them.
"Under these circumstances, we will not participate in the planned Sochi summit. We will suspend our participation in the G8 until Russia changes course and the environment comes back to where the G8 is able to have a meaningful discussion and will meet again in G7 format at the same time as planned, in June 2014, in Brussels, to discuss the broad agenda we have together.
"We have also advised our foreign ministers not to attend the April meeting in Moscow. In addition, we have decided that G7 energy ministers will meet to discuss ways to strengthen our collective energy security."
The leaders of the G7 - US, UK, Germany, France, Italy, Canada and Japan along with the European Union - met in The Hague on the sidelines of a summit dealing with measures to tackle nuclear terrorism.
Following talks at the Catshuis, the official residence of Dutch prime minister Mark Rutte, the leaders repeated their condemnation of Russia's actions and the "illegal" annexation of Crimea.
In a joint statement they indicated they were ready to "intensify" sanctions if Moscow took further action in neighbouring Ukraine, warning that it would have an "increasingly significant impact" on Russia's economy.
They said: "International law prohibits the acquisition of part or all of another state's territory through coercion or force. 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. We do not recognise either.
"Today, we reaffirm that Russia's actions will have significant consequences. 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.
"In response to Russia's violation of Ukraine's sovereignty and territorial integrity, and to demonstrate our determination to respond to these illegal actions, individually and collectively we have imposed a variety of sanctions against Russia and those individuals and entities responsible.
"We remain ready to intensify actions including co-ordinated sectoral sanctions that will have an increasingly significant impact on the Russian economy, if Russia continues to escalate this situation."
The meeting of G7 energy ministers is a potentially significant development, alongside European efforts to wean itself off dependency on Russian oil and gas.
Before the meeting, which took place as dignitaries gathered in The Hague for the Nuclear Security Summit, Mr Cameron warned Mr Putin that a fresh round of sanctions would follow if his forces marched any further into Ukrainian territory.
Concerns remain about Russia's military ambitions in Ukraine following the intervention in Crimea, with Nato's supreme commander warning that Moscow had deployed a "very, very sizeable and very, very ready" force on the country's border.
US General Philip Breedlove raised the prospect that the Kremlin could even seek to take control of a Russian-speaking section of nearby Moldova.
Mr Cameron said: "These reports are concerning and we need to send a very clear message to the Russian government and to president Putin that it would be completely unacceptable to go further into Ukraine, and that would trigger sanctions from the EU, from the US, from other countries as well.
"We need to be very, very clear about that."
But in a sign that there could be diplomatic progress towards resolving the crisis, Russian foreign minister Sergey Lavrov met his Ukrainian counterpart Andriy Deshchytsia for face-to-face talks for the first time.
The Russian ministry of foreign affairs posted a picture of the two men meeting at The Hague on its Twitter feed.
Mr Lavrov appeared unmoved by the G7's actions against Moscow, saying: "The G8 is an informal club, no one gives out membership cards and no one can expel members."
Russia Today reported that he said: "If our Western partners believe that this format has exhausted itself, let it be. We are not clinging to it."
Ukraine's decision to pull its remaining personnel out of Crimea follows a series of operations by Russian forces to seize Ukrainian ships and military installations in the strategically important peninsula.
Acting president, Oleksandr Turchnynov, whose new government has struggled to maintain control and cohesion, said the defence ministry was ordered to withdraw all servicemen in Crimea to Ukraine's mainland.
Russia completed its annexation of Crimea last week after its troops took control over the Ukrainian region following the removal of a Kremlin-friendly government in Kiev.
Moscow says its absorption of Crimea has been rendered legitimate by a referendum, but Mr Cameron and other Western leaders have refused to recognise the result.
Foreign Secretary William Hague said it was a "huge blow" for the G8 and it would be hard to revive the relationship with Russia.
He said: "It's of course a huge blow to the G8, it means there is no G8 this year. The president of the United States was very clear in the meeting that it will then be hard to revive that in the immediate future.
"It would need our values to be clear, our shared values to be clear again, and clearly those shared values are not shared by Russia in violating the independence and territorial integrity of a neighbouring nation state.
"This is the G7 this year and we will see how long it takes to change that in the future."
He highlighted the focus on energy issues as potentially "changing the balance of leverage between Russia and the European Union".
He acknowledged that tougher sanctions would mean "many countries bear the cost of that in many ways" but "we have to be prepared to do that".
Mr Hague said: "Every country would have to do what is necessary if more far-reaching sanctions were applied, accepting that that would affect different economies in different ways.
"The United Kingdom is certainly prepared to do that. There is nothing that other countries in Europe have proposed that we have blocked. The United Kingdom is fully prepared to play its full part."
Responding to Mr Lavrov, Mr Hague said: "Judging by tonight's meeting, the G7 will take on an extra importance because the determination of the leaders there tonight that they condemn what has happened in Crimea and their determination particularly to discuss energy together - and they came back again and again to this in their discussions during the course of the evening - their determination to work on energy diversification is something that is, of course, of importance to Russia as well as being of importance to all of them."