U.N. nuclear agency inspectors returned to Iran Saturday for the first time since Tehran reversed a decision to bar them because of allegations the country was hiding some banned activity.

The International Atomic Energy Agency (search) inspectors will inspect two nuclear facilities and quiz top Iranian officials on the country's atomic program. They are trying to verify Iran's claims that its nuclear activity is for peaceful purposes only.

IAEA spokeswoman Melissa Fleming told The Associated Press in Vienna that the inspectors have already begun their work.

Two weeks ago, Iran had barred inspectors after the IAEA issued a report rebuking the country for failing to disclose certain aspects of its nuclear development, as it is obliged to do as a signatory to the Nuclear Nonproliferation Treaty.

The United States accuses Iran of pursuing a nuclear weapons program, and Washington has called for Iran to suspend all uranium-related activity. Iran suspended enrichment last year under strong international pressure over the aims and dimensions of its nuclear program.

But Iran says the suspension is only temporarily, and insists it wants atomic energy only for peaceful purposes.

The IAEA inspectors are expected to meet with top officials from Iran's atomic agency. The team will also visit nuclear facilities in the central Iranian cities of Isfahan and Natanz.

Earlier Saturday, Iran announced that it recently inaugurated the Isfahan nuclear facility, which processes uranium ore into gas — a crucial step before uranium enrichment.

"The uranium conversion facility started working some time ago now," a senior official at Iran's Atomic Energy Organization (search) told The Associated Press on condition of anonymity.

Enriched uranium can be used for atomic energy or to make bombs.

Iran continues to assemble centrifuges for enriching uranium, despite criticism that this violates the spirit of its pledge to suspend the process.

Mohammed ElBaradei (search), director of the IAEA, has said Iran needs to take many steps before the U.N. agency can give its nuclear program a clean bill of health.

Suspicion of Iran's program heightened last year when the IAEA revealed that its inspectors had found radioactive particles that had been enriched to weapons-grade level — higher than what Iran requires for fuel for a nuclear reactor.

Iran said the particles had been found on imported equipment.

ElBaradei, who plans to visit Iran early next month to encourage it to be more transparent, hopes to present an assessment of Iran's nuclear activities to the IAEA board of governors in June.