Rice demanded a response despite the country’s nuclear negotiator warning he would not give Iran’s final answer on Tuesday to the top EU diplomat at a meeting where the powers hope for a formal reply.
"It is really time to get an authoritative answer to that proposal," Rice said at a joint news conference with Foreign Secretary Margaret Beckett.
In early June, major powers offered negotiations, which would include the United States for the first time, if Iran suspended enrichment activity that the West suspects is used in the pursuit of a nuclear bomb. Iran says it only seeks to develop power generation.