A day after canceling a trip by U.N. atomic inspectors to two Iranian nuclear plants, Tehran said Saturday it will renew its invitation to visit the plants, which the United States says belong to a secret nuclear weapons program.

"Tehran will officially invite IAEA (International Atomic Energy Agency) experts to visit the nuclear plants at Natanz and Arak," state-run radio quoted Foreign Minister Kamal Kharrazi as saying. He did not specify a date for the visit.

On Friday, the chief of the Vienna-based IAEA, Mohamed ElBaradei, said Iranian officials had told him he could not visit the sites as planned this week because President Mohammad Khatami would be out of the country and "they need some time to prepare."

As a result, the inspection has been rescheduled for February, ElBaradei told reporters in Austria. No IAEA comment was immediately available on Iran's decision to renew its invite.

The United States has long been suspicious about Iran's nuclear program, accusing it of sponsoring terrorism and labeling it — along with Iraq and North Korea — as part of an "axis of evil."

On Friday, U.S. State Department spokesman Richard Boucher said satellite imagery indicated that some structures at the Natanz plant in central Iran were being covered with earth, indicating Tehran is building "a secret underground site where it could produce fissile material."

"Iran clearly intended to harden and bury that facility," Boucher said. "That facility was probably never intended by Iran to be a declared component of the peaceful (nuclear) program."

Iranian government spokesman Abdollah Ramezanzadeh rejected Boucher's charges, saying Natanz "is not under the ground" and that "all our nuclear sites are for peaceful purposes and open to IAEA inspection."

"We have no nuclear activity or study without the knowledge of the International Atomic Energy Agency," Ramezanzadeh said.

ElBaradei, the IAEA chief, has said he learned six months ago that Tehran was expanding nuclear facilities — three months before Tehran officially notified him in September.

Kharrazi on Saturday said the two nuclear sites are intended to generate electricity during the next two decades. Iran has no plans to produce nuclear weapons and that "all our programs are for peaceful purposes," he said.

Much of the public attention given to Iran's nuclear effort focuses on a power reactor at Bushehr, which is being built with Russian assistance. The power station in southern Iran is supposed to go on line at the end of the year.