In their final communique from a three-day annual summit, the G8 said: "We deplore the fact that Iran has so far failed to meet its obligations" under UN Security Council resolutions on its nuclear programme.

It said it "will support adopting further measures, should Iran refuse to comply with its obligations."

"We again urge Iran to take the steps required by the international community, and made mandatory by these resolutions, to suspend all its enrichment-related and reprocessing activities, including research and development, and allow negotiations to begin," the communique added.

The G8 -- Britain, Canada, France, Germany, Italy, Japan, Russia and the United States -- also said that international confidence in the exclusively peaceful nature of the Iranian nuclear programme would permit a "completely new chapter to be opened" in relations with Iran, in the nuclear and other fields.