"If they do not, the international community is united that more sanctions are coming," U.S. National Security Council spokesman Gordon Johndroe said.
Hours before Johndroe made the remarks, Iranian President Mahmoud Ahmadinejad said that Iran will not make any concession in the country's nuclear rights.
But he also said that "We have announced our readiness for talks with all countries except the Israeli regime."
The package of incentives offered by the United States, Russia, China, Britain, France and Germany last month over the resumption of nuclear negotiations, suggests that Iran get a temporary reprieve from economic and financial sanctions in exchange for freezing its enrichment activities. Preliminary negotiations over a permanent halt could then begin.
European Union (EU) foreign policy chief Javier Solana and Iranian top nuclear negotiator Saeed Jalili held nuclear talks in Geneva on Saturday.
U.S. Undersecretary of State William Burns and senior diplomats from the other five powers attended the talks.
During the one-day meeting, Iran failed to give a clear answer to the package of incentives. However, both Solana and Jalili said the meeting was positive and constructive and promoted understanding of each other's positions. They also agreed to talk again by phone or in person in about two weeks.
