United Nations: The United States on Tuesday threatened to push quickly for economic sanctions against Iran in the UN Security Council if it fails to heed demands for a freeze of its uranium enrichment activities.

As Iran delivered its long-awaited response to an international deal aimed at ending a nuclear standoff, US Ambassador to the UN John Bolton said: "This is a significant moment. We will obviously study the Iranian response carefully, but we are also prepared, if it does not meet the terms set [by six major powers], to proceed here in the Security Council ... with economic sanctions".

"I think we will be prepared to submit elements of a resolution in the council very quickly," he said.

"The rhetoric, particularly in the past few days, has indicated they [Iranians] are not prepared to suspend their uranium enrichment activities, but we have consistently said for two and a half months that we would not rise to the rhetoric, we would wait for the definitive response," Bolton said.

Top nuclear negotiator Ali Larijani delivered Tehran's written response shortly after 1315 GMT to representatives of the five permanent Security Council members Britain, China, France, Russia and the United States plus Germany.

Details of the Iranian response were not immediately available, but the student ISNA news agency quoted Larijani as telling the envoys that Tehran was "ready for serious talks with the 5+1 group from August 23 over the offered package".

"Although there is no justification for the other parties' illegal move to refer Iran's case to the Security Council ... the answer was prepared to pave the way for fair talks," Larijani said.

He said Iran was ready to play a "constructive" role regarding all issues. One European diplomat said: "It is a comprehensive answer. The Iranian side said they would welcome a continuation of negotiations."

World powers have offered a package of economic and political incentives in exchange for a freeze of Iran's uranium enrichment.1997 to 2005, would be the most senior Iranian to visit the United States since Washington broke off diplomatic relations following the Islamic revolution in 1979.

He has been invited to speak next month on "understanding between civilisations and cultures" at the Washington National Cathedral, the event organiser said.