The five permanent UN Security Council members and Germany have been leading efforts to persuade Tehran to abandon its nuclear programme.
The countries’ foreign ministers agreed on Friday to begin consultations on possible UN sanctions against Iran.
The talks could start next week, though China and Russia favour more diplomacy.
Western powers fear that Iran is seeking to develop nuclear weapons, a charge Iran denies saying that it is simply trying to develop nuclear energy.
A statement agreed in London on Friday after a meeting between foreign ministers from the five permanent UN Security Council members and Germany said the six powers will now discuss unspecified measures to be taken against Tehran.
‘Always open’
BBC correspondent Jonathan Beale says Washington believes the decision to impose sanctions has now been taken.
According to our correspondent, a senior US diplomat had confirmed talks would begin early next week on economic sanctions to be used against Tehran.
But Russia played down the significance of the deal saying that no-one was talking about a vote in the UN Security Council in the immediate future.
The six nations had offered Iran a package of incentives in return for the suspension of its uranium enrichment programme.
EU foreign policy chief Javier Solana was present to brief ministers on his talks with Iran.
He said earlier that “the door to negotiations is and will be always open”, despite saying earlier this week that little progress had been made in his “endless hours” of talks with Tehran.
