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, Reuters reports.

"It is really time to get an authoritative answer to that proposal," Rice said at a joint news conference with Foreign Secretary Margaret Beckett.

Rice, Beckett and their counterparts from China, Russia, France and Germany will meet on Wednesday in Paris to work out a strategy for how to deal with Iran, although they may have no definitive answer whether Tehran accepts the terms for talks.