WASHINGTON—In a break with past Bush administration policy, a top U.S. diplomat will for the first time join colleagues from other world powers at a weekend meeting with Iran’s chief nuclear negotiator, The Associated Press has learned.

William Burns, America’s third highest-ranking diplomat, will attend talks with the Iranian envoy, Saeed Jalili, in Switzerland on Saturday aimed at persuading Iran to halt activities that could lead to the development of atomic weapons, a senior U.S. official told the AP on Tuesday.

Official contacts between Iran and the United States are extremely rare and although Washington is part of a six-nation effort to get Iran to stop enriching and reprocessing uranium, the administration has shunned contacts with Tehran on the matter. The senior U.S. official, who spoke on condition of anonymity ahead of a formal announcement of Burns’ plans expected on Wednesday, acknowledged a shift in the administration’s approach but stressed that Burns would not meet Jalili separately and would not negotiate with him. “This is a one-time event and he will be there to listen, not negotiate,” the official said.

The meeting in Geneva is being led by European Union foreign policy chief Javier Solana, who is seeking a definitive answer from the Iranians to an offer of incentives that the five permanent members of the U.N. Security Council and Germany presented last month. The package of incentives was accompanied by a letter from Secretary of State Condoleezza Rice and the foreign ministers of the other five countries and sets out a scenario in which Iran would get a temporary reprieve from crippling economic and financial sanctions in exchange for freezing its enrichment activities. Preliminary negotiations over a permanent halt could then begin, although the United States would not join them until after Iran agrees to fully suspend uranium enrichment, which can produce the fuel needed to make nuclear bombs.