State Department spokesman Sean McCormack accused Tehran of "inspector shopping" and of trying to "dictate" to international bodies by demanding the ouster of Chris Charlier, a Belgian citizen.
Iran this week banned 38 inspectors from the UN's International Atomic Energy Agency (IAEA) from working in Iran to monitor Iranian nuclear facilities.
"The New York Times" today quoted IAEA Director-General Muhammad el-Baradei as saying in Vienna on January 26 that Iranian officials have said they expect to start installing equipment in February at an industrial-scale uranium-enrichment plant.
The UN Security Council imposed sanctions against Iran in late-December based on a report by the IAEA, which has repeatedly expressed frustration over a lack of disclosure by Iran of its nuclear activities. The IAEA has blamed Tehran for failing to provide sufficient evidence to demonstrate that its nuclear program is purely peaceful.
The United States and some Western allies have accused Iran of seeking to develop nuclear weapons, a charge that officials in Tehran consistently reject.
Pyongyang Denies Nuclear Cooperation
Meanwhile, North Korea today dismissed allegations that it is cooperating with Iran in nuclear development.
The Foreign Ministry said in a statement carried by North Korea's official Korean Central News Agency that the "assertion is nothing but a sheer lie" intended to tarnish Pyongyang's image by charging it with nuclear proliferation.
The ministry also said the North will continue to honor its duty in the field of nuclear nonproliferation as a responsible nuclear weapons state.
A North Korean announcement in October of a successful nuclear test spread alarm and demonstrated that international efforts had failed to prevent that country's nuclear weapons efforts from coming to fruition.
THE COMPLETE PICTURE: RFE/RL's complete coverage of controversy surrounding Iran's nuclear program.
An annotated timeline
of Iran's nuclear program.