The announcement was a tacit rebuff to a deal brokered by Brazil and Turkey and made public on Monday in which Iran agreed to send some uranium abroad. U.S. officials regard that deal as a maneuver by Iran to delay more U.N. sanctions.

"This announcement is as convincing an answer to the efforts undertaken in Tehran in the last few days as any that we could provide," Clinton added, repeating that Washington has many questions about the fuel swap deal.

The deal had revived the idea of a nuclear fuel swap devised by the United Nations last year with the aim of keeping Tehran's nuclear activities in check.

But Tehran made clear it did not intend to suspend domestic uranium enrichment that Western governments have said appears aimed at giving it the means to make nuclear weapons.

Western nations have reacted skeptically to the deal, although China -- the major power most reluctant to impose more sanctions on Iran -- welcomed it and urged talks with Tehran.

Clinton told lawmakers in Washington: "We have reached agreement on a strong draft with the cooperation of both Russia and China." She gave no details of the draft, but said it would be circulated to the full Security Council later on Tuesday.

She said the agreement was reached among the five permanent Security Council members -- Britain, China, France, Russia and the United States -- and Germany, which have been engaged in talks on ways to address any nuclear threat from Tehran.

The Security Council will hold a closed-door session on Tuesday afternoon to receive the draft, diplomats said, and the United States is looking to get the maximum backing in the 15-member council.