The industrial powers — Britain, Canada, France, Germany, Italy, Japan, Russia and the United States — said they "strongly urge" Iran to cooperate fully with the UN International Atomic Energy Agency.
"We also urge Iran to act in a more responsible and constructive manner in the region, particularly in the context of the Middle East peace process and the stability of Iraq and Afghanistan," said a statement after talks in Japan.
Western powers have been ramping up pressure on Iran for refusing to suspend sensitive uranium enrichment, a process which can be used in the manufacture of nuclear weapons.
Tehran denies wanting to make an atomic bomb, saying its nuclear programme is purely peaceful and to generate electricity.
Former president Akbar Hashemi Rafsanjani slammed what he called the "double-speak" approach of the superpowers, saying it would lead to failure.
"Today in Japan the members of the G8 group have adopted another resolution to apply a carrot and stick policy," he said in a Friday prayers speech in Tehran broadcast over state radio.
"This type of double-speak will not help you and will not lead to a solution" to the nuclear problem, he said, addressing the Western powers.
"You are too small to use this type of language. Iran is a large country… the language of dialogue and negotiation must be used," he added.
Rafsanjani, who was defeated by Iranian President Mahmoud Ahmadinejad in 2005 presidential elections, retains a considerable powerbase as head of both Iran's top arbitration body the Expediency Council, and the elite clerical Assembly of Experts.
On Monday the European Union approved sanctions aimed at operations by Bank Melli, Iran's largest financial institution, in Britain, France and Germany — the three EU countries negotiating with Tehran.
The Islamic republic has defied UN sanctions and international demands by pressing on with its disputed uranium enrichment programme, which both Washington and Israel fear will be used for military purposes.
Speculation about a possible Israeli strike against Iran was rife this week after Washington's former UN envoy John Bolton suggested in an interview with London's Daily Telegraph that Israel could attack between the November 4 US presidential election and January.
According to the US television network CBS, Israel does not want to wait until the new administration that succeeds President George W. Bush in January before targeting Iranian nuclear sites.
"The Israelis have been assured by the Bush administration that the Bush administration will not allow Iran to nuclearise," CBS consultant Michael Oren said.
"Israelis are uncertain about what would be the policies of the next administration vis-a-vis Iran," added Oren, a senior fellow at the Shalem Centre, a Jerusalem-based research facility.
