Britain warned President Vladimir Putin that Russia could face permanent exclusion from the G8 if the Kremlin took further steps against Ukraine.
"I think we should be discussing whether or not to expel Russia permanently from the G8 if further steps are taken," Prime Minister David Cameron told the British parliament yesterday.
The United States and its G7 allies will gather next week at The Hague without Russia to consider a further response to the Kremlin's moves to annex Crimea.
The EU agreed earlier this week to impose asset freezes and travel bans on 21 individuals linked to the action in Crimea.
"If we turn away from this crisis and don't act we will pay a very high price in the longer term," Cameron said.
US Vice-President Joe Biden, speaking in Warsaw, said the United States may run more ground and naval military exercises to help Baltic states near Russia beef up their capacity and reassure Nato allies.
Biden, in the Polish capital on the first leg of a two-day trip to the region, criticised Russia's actions as a land grab, and called Nato's commitment to protect its members from attack as unwavering.
"We are exploring a number of additional steps to increase the pace and scope of our military co-operation, including rotating US forces to the Baltic region to conduct ground and naval exercises and training missions," he said after talks in Warsaw with Toomas Hendrik Ilves, Estonia's president.
A senior administration official said details about the proposed military exercises would come later. "This would not be a fundamental expansion, or crossing of a basic line, so to speak," the official said.
"It's more an opportunity to enhance our capacity to do training with them in the region."
Russia said it sent troops into Crimea to protect Russian residents it alleged were in danger since Viktor Yanukovych, Ukraine's pro-Russian president, was forced out of office.
Sunday's referendum in Crimea saw residents support becoming part of Russia, but Western leaders called that vote a Moscow-orchestrated sham.
Biden said events in Crimea showed Nato members they needed to stand together.
Washington would take extra steps to strengthen Nato, he said. These would include the US standing by its commitment to complete a missile defence system in Poland by 2018.
"Recent events remind us the bedrock of our alliance remains collective self-defence as enshrined in Article 5 of the Nato treaty," Biden said.
"We take it deadly serious and our commitment is absolutely unwavering and unshakeable."
The three Baltic states of Estonia, Latvia and Lithuania are in Nato and the European Union. But they are small, depend on Russia for energy and trade, and have sizeable Russian-speaking minorities, so all are particularly vulnerable to any Russian military action.
Biden also said that the US wanted to help eastern European states find ways to reduce their dependence on imported Russian fuel, which - US officials claim - the Kremlin uses as a way to exert political influence.