Tehran:
Four inspectors of the United Nations International Atomic Energy Agency arrived in Tehran early on Sunday to check Iran's controversial second uranium enrichment plant.
The plant is being constructed inside a mountain near the holy city of Qom south of Tehran.
The inspectors were due to visit the site on Sunday, two days after Tehran postponed its response to a UN deal on supplying the Islamic republic with nuclear fuel.
Media reports said the team would spend three days in the country to inspect the facility being built some 100 km south of the capital.
Tehran's disclosure of the new plant to the IAEA on September 21 triggered widespread global outrage, with US President Barack Obama warning Iran would face "increased pressure" if it does not come clean on its nuclear activities.
IAEA chief Mohamed ElBaradei criticised Tehran for what he said was its late disclosure of the facility's existence.
Uranium enrichment lies at the heart of Western concerns about Iran's nuclear programme. It produces fuel for civilian reactors, but in highly extended form can also make the fissile core of an atomic weapon.