Two inspectors from the International Atomic Energy Agency arrived in Iran to inspect the Islamic republic's nuclear facilities, the official IRNA news agency said.
The announcement came after Iran's parliament urged the government late December to re-examine its ties with the UN Nuclear agency following a Security Council decision to impose sanctions against Tehran over its disputed nuclear programme.
Iran says that as a signatory to the Nuclear Nonproliferation Treaty it has the right to develop a peaceful uranium enrichment programme to produce nuclear power.
But the UN Security Council voted in December to impose limited sanctions on Iran for its refusal to cease enrichment of uranium - a process that produces the material for either nuclear reactors or atomic bombs.
The United States and its European allies suspect Iran's civilian nuclear programme is a cover for developing such a bomb. Iran says its programme is strictly for generating electricity.
The official IRNA news agency said on Wednesday that the two IAEA inspectors were conducting routine investigations in Iran's nuclear facilities.
"The inspectors arrived in Iran on Wednesday and they have already visited uranium conversion facilities in central city of Isfahan," the state news agency said, quoting an unnamed official.
"Inspectors will stay for one week to inspect facilities in Isfahan and Natanz, IRNA said.
The state agency said the IAEA inspectors would also "review the trend of cooperation with Iranian nuclear officials.