However, Iran warned Wednesday it would not tolerate "spying" at the Parchin military facility which had previously been off limits to inspectors from the International Atomic Energy Agency (IAEA).

The IAEA visit coincides with the resumption of EU talks on a trade accord with Iran, 18 months after they were suspended due to concerns about Tehran's nuclear plans.

The negotiations on a trade and cooperation agreement were restarted after the Iran agreed to suspend uranium enrichment in an accord thrashed out following intense pressure, notably from the United States.

But the resumption was clouded by a reported announcement from Tehran that Iran plans to resume uranium enrichment soon.

The IAEA team arrived in Tehran Wednesday and is due to stay in the country for a week, student news agency ISNA reported.

Tehran gave permission for inspectors to take so-called environmental samples from the massive Parchin site around 30 kilometers (20 miles) southeast of Tehran in order to disprove US allegations of secret weapons-related activities.

Washington has voiced concern that the Iranians may be working on testing high-explosive charges with an inert core of depleted uranium at Parchin as a sort of dry test for how a bomb with fissile material would work.

A US official told AFP earlier this month that the testing in Parchin may "amount to (nuclear) weapons intent".

Tehran has strongly denied carrying out any nuclear-related work at the site, and insists its nuclear drive is merely aimed at generating electricity and that it is not developing atomic weapons.

"We are watchful. We have allowed inspections into our military installations but we will not allow any espionage or the theft of information from our military sites," Hossein Mousavian, the spokesman for Iran's nuclear negotiations team, said in remarks carried by the conservative Mehr news agency Wednesday.

"It is not necessary for the inspectors to enter the installations. They are authorized to take samples outside (the buildings) using their equipment."

Parchin is an example of a so-called "transparency visit" where the IAEA is going beyond its mandate under the nuclear Non-Proliferation Treaty (NPT) to check if nuclear materials have been diverted away from peaceful use.

IAEA chief Mohamed ElBaradei announced last week that Iran had finally given the green light for his inspectors to probe Parchin after seeking access to the site since July.

Environmental sampling involves taking swabs or soil samples to detect the presence of nuclear activity.

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