Iranian officials did not directly respond to the package agreed on a day earlier by the five permanent members of the UN Security Council, plus Germany, which calls on Iran to suspend uranium enrichment. Details of the offer have yet to be formally presented to Teheran.
But Iran's top nuclear negotiator, Ali Larijani, said Europe should "leave out excuse-seeking and illogical conditions and come back to negotiations and cooperation."
"Iran is ready for any unconditional, just and non-discriminatory negotiations," he was quoted as saying by state-run television.
Hard-liner President Mahmoud Ahmadinejad also struck a defiant note, vowing that "the efforts of some Western countries to deprive us will not bear any fruit."
"The reason of their opposition is not their claim of concern over nuclear weapons, but Iran's access to the technology that means opening of the way for all independent countries, especially Islamic countries to the advanced technology," he was quoted as saying by the state news agency IRNA.
The United States warned Iran it will not have much time to respond once offered the international package of rewards, suggesting that the window could close and be replaced by penalties if it doesn't act quickly.
"It really needs to be within weeks," US 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.
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, US 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 Teheran. A senior US state department official said he expected Teheran 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.
In Moscow, Russian Foreign Minister Sergey Lavrov said Friday that Teheran "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 Teheran agrees to suspend activity that can lead to the production of nuclear arms, and to negotiate the details of the deal.
German Foreign Minister Frank-Walter Steinmeier said Friday that signs for success were strong: "We are hopeful that the Iranian side, acting with a sentiment of responsibility and fastidiousness, will examine the proposal and that a positive approach will emerge," he told a joint news conference with his Turkish counterpart, Abdullah Gul, during a visit to Ankara.
"The fact that the United States will sit at the table is important," Steinmeier said. "We hope that the two countries will reach such a decision."
US Undersecretary of State Nicholas Burns on Thursday called the meeting's outcome "a step forward in our quest to deny Iran nuclear weapons capability."
The group's statement contained no details of incentives Iran could be offered, and only threatened unspecified "further steps" in the Security Council if Teheran refuses them. Diplomats previously have said the package includes help to develop legitimate nuclear power plants and various economic benefits.