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Iran is reported to have rejected a United Nations-brokered uranium enrichment plan.

A Western official close to the negotiations with Tehran says Iran told the U.N.'s International Atomic Energy Agency that it will not accept the plan to ship its uranium abroad for low-level enrichment.

Meanwhile, Iran says it has not yet given its response to the IAEA plan. The state-run IRNA, Iranian Republic News Agency, says Tehran had only expressed its "positive" viewpoint on negotiations and is willing to continue to hold talks. The news agency quoted an unidentified official Friday.

The IAEA proposal is aimed at preventing Iran from enriching uranium to the point that it can be used for nuclear weapons. It has already been agreed to by the other parties involved in the negotiations - the United States, Russia and France.

White House spokesman Robert Gibbs says President Barack Obama's time is not "unlimited" when it comes to nuclear talks with Iran.

Gibbs said the negotiations are not about "talking for the sake of talking" but about reaching an agreement.

European Union leaders Friday urged Iran to accept the deal, saying this would help "build confidence."

The U.N. Security Council has imposed three sets of sanctions on Iran for its refusal to halt its enrichment activities.

Some information for this report was provided by AFP, AP and Reuters.