The United States said it would give European negotiator Javier Solana more time for talks on the nuclear issue with Iran, in a concession to Washington's major-power partners.
But US Undersecretary of State Nicholas Burns insisted major-power foreign ministers, at a two-hour meeting, reaffirmed support for sanctions if Tehran does not suspend uranium enrichment, although they still had not agreed on specific penalties.
"The United States is willing to support Solana's discussions" with Iranian negotiator Ali Larijani, which are continuing beyond an August 31 UN deadline for Iran to halt enrichment, Mr Burns told reporters.
"If Iran does not suspend, then we will fulfill (UN Security Council resolution) 1696 and adopt sanctions measures under article 41 of the UN Charter," he said after a meeting of foreign ministers of the United States, Britain, France, Germany, Russia, and China.
Italy also attended, because part of the discussion focused on Lebanon, where Italy has committed to send peacekeeping troops. It also hosted a Lebanon conference in July in Rome.
Mr Burns declined to say how long the United States, the prime advocate of sanctions, was willing to wait for Mr Solana's talks with Larijani to bear fruit. US officials said the major powers had a set deadline.
"There will come a time shortly, but I will not put a date on it, when we're going to have to see an unequivocal answer," Mr Burns said.