Iran has rejected an appeal from the head of the International Atomic Energy Agency to suspend its uranium enrichment activities.
Iran's top nuclear negotiator Ali Larijani met with IAEA chief Mohamed ElBaradei in Tehran Thursday. Afterward he said such demands are not important.
ElBaradei said Iran reiterated its promise to clarify outstanding issues regarding its nuclear program. He said he has yet to confirm Iran's claim of enriching uranium to a level used in nuclear power plants - a breakthrough Tehran announced Tuesday.
In Washington, U.S. Secretary of State Condoleezza Rice said Iran could face escalating international penalties if it ignores a U.N. Security Council demand to halt its nuclear work. She said one option is the chapter seven resolution of the U.N. charter, which could allow for sanctions against Iran.
Last month, the Security Council gave Iran 30 days to suspend uranium enrichment. The IAEA chief is expected to report to the U.N. body on Iran's compliance by April 28.
The United States accuses Iran of running a secret nuclear weapons program - a charge Tehran denies.
China's Assistant Foreign Minister Cui Tiankai is to begin Friday, a trip to Iran and Russia in an attempt to defuse the Iranian nuclear issue.