U.S. Undersecretary of State William Burns will join European Union foreign-policy chief Javier Solana and envoys from China, Russia, France, Britain, and Germany to attend talks with Iran's top nuclear negotiator, Saeed Jalili, in Geneva on July 19.
Burns, the third-highest ranking U.S. diplomat, will not hold separate talks with Jalili and will be there "only to listen," according to U.S. officials.
The move signals a significant shift in U.S. President George W. Bush's tough stance toward Iran's alleged pursuit of nuclear weapons and comes after Washington insisted it would only negotiate with Iran if it suspended its nuclear-enrichment activities, something Tehran has refused to do.
Although Washington is part of a six-nation effort to get Iran to stop enriching uranium, the Bush administration has avoided official contacts with Tehran on the matter.
'Interesting Diplomatic Approach'
Diplomatic relations between Washington and Tehran were broken after the 1979 Iranian Revolution and the taking of hostages at the U.S. Embassy in Tehran.
Ali Ansari, an Iran expert at the London-based think tank Chatham House, calls the move "an interesting diplomatic approach." He says its significance will become clearer after the talks.
"I think that the red lines that both sides have defined about uranium enrichment weren't bad at all for the time being," Ansari said. "I think what you are going to find is that a lot of these maneuvers at the moment are also for public consumption. So it's interesting to see that the United States at the moment is moving in a particular direction and wants to show -- particularly Bush wants to indicate that he is keen to explore every diplomatic option. And we have to wait and see what happens from the Iranian side."
The Geneva meeting comes after last month's talks in Tehran where Solana again put forward a package of proposals designed to help Iran develop a civilian nuclear program.
Tehran has repeatedly refused to give up its uranium-enrichment activities, saying it is only for peaceful purposes.
The move is likely to scramble the foreign-policy debate in the U.S. presidential election. John McCain, the presumptive Republican nominee, has sided with the administration in arguing that the United States should sharply limit contacts with Tehran.
Barack Obama, the likely Democratic nominee, has said he is willing to begin high-level talks with Iranian leaders, provided certain conditions are met.
Iranian President Mahmud Ahmadinejad said on July 15 that the next U.S. administration has "no other option" but to begin talks with Tehran.
"Tehran welcomes negotiations but will not accept the precondition set by the West -- the suspension of uranium enrichment," he was quoted as saying in a television interview.
Three Rounds Of Sanctions
The UN Security Council has adopted three rounds of economic sanctions against Iran because of its refusal to suspend enrichment.
The six world powers have offered economic and other incentives to coax Tehran into halting sensitive nuclear work that the West fears is aimed at making bombs. Up to now, Tehran has repeatedly refused the offer and declared that under no circumstances will it give up enrichment.
The July 19 meeting in Switzerland comes just days after Iranian missile tests last week that increased tension between Tehran and Washington, prompting the United States to warn that it will defend its interests and its allies in the region against any threat from Iran.
If a temporary end to enrichment was started, preliminary negotiations on a permanent halt could begin, although the United States would not join such talks until a full suspension of uranium enrichment was declared by Iran.
RFE/RL's Radio Farda contributed to this report.