US warns: Iran will not have much time to think over US offer in nuclear sphere

"It really needs to be within weeks," U.S. Secretary of State Condoleezza Rice told NBC television, referring to a response to a package of perks and penalties from six world powers aimed at halting Iran's enrichment activities.

The package, agreed upon Thursday by the five permanent members of the U.N. Security Council and Germany, carries the threat of U.N. sanctions if Tehran remains defiant over what the West calls a rogue nuclear program that could produce a bomb.

A short statement issued Thursday night did not mention economic sanctions, but officials said privately that Iran could face tough Security Council sanctions if it refuses to give up uranium enrichment and other disputed nuclear activities, U.S. officials said.

The formal offer of talks is expected to be made by France, Britain and Germany - the three EU nations that previously negotiated with Tehran. A senior U.S. state department official said he expected Tehran would be invited to begin new negotiations "within a matter of days."

Russia and China, which both hold vetoes in the Security Council, might also join in any future talks with Iran, the AP reports.

In Moscow, Russian Foreign Minister Sergey Lavrov said Friday that Tehran that Iran "will not face a deadline to respond to the proposal of the six nations" - but said he expected Iran to give an answer within a few weeks of receiving the offer, the ITAR-Tass news agency said.

The United States, in a major policy shift, conditionally agreed this week to join those talks. It would be the first major public negotiations between the two countries in more than 25 years.

Rice suggested in separate comments to National Public Radio that she was ready to meet her Iranian counterpart, Manouchehr Mottaki, if Tehran agrees to suspend activity that can lead to the production of nuclear arms, and to negotiate the details of the deal.