Britain will suspend its participation in preparations for a G8 meeting in Sochi after Russia violated Ukraine's sovereignty and territorial integrity, British Foreign Minister William Hague said on Sunday.
The United States has already said it will not take part in the meetings, and a source in President Francois Hollande's office said France has also pulled out.
Western countries are scrambling to respond to developments in Ukraine's Crimea, where Putin has claimed the authority to send Russian troops in the biggest confrontation between Moscow and the West since the Cold War.
"The United Kingdom will join other G8 countries this week in suspending our co-operation under the G8, which Russia chairs this year, including ... meetings this week for the preparation of the G8 summit," Hague told media before boarding a flight to Kiev to meet with the pro-Western government that took power when Russian ally Viktor Yanukovich fled last week.
Hague said Russia would have to "think hard" about the united diplomatic and peaceful international response to its actions and said he hoped direct communication between Ukraine and Russia would be able to take place.
"We call on both sides to ensure that there can be a reduction in tensions and the avoidance of conflict," he said.
Canada said Saturday that it was recalling its ambassador to Moscow and pulling out of preparations for the summit.