Iran will grant U.N. inspectors access to a military complex where the U.N. nuclear agency suspects secret atomic work has been carried out, the semi-official ISNA news agency reported Tuesday.

Tehran had previously banned U.N. inspectors from visiting the Parchin installation, southeast of Tehran, but a statement by Iran's permanent envoy to the International Atomic Energy Agency said the visit will now be allowed in a gesture of good will.

However, it would require an agreement between the two sides on a guidelines for the inspection, ISNA reported.

Inspecting Parchin was a key request made by senior IAEA teams that visited Tehran in January and February. Iran rebuffed those demands at the time, as well as attempts by the nuclear agency's team to question Iranian officials and secure other information linked to the allegations of secret weapons work.

The latest development comes a day after IAEA chief, Yukiya Amano, expressed growing concern that there was new activity at Parchin. Amano did not specify whether he believed the activity was linked to suspected new weapons experiments or attempts to clean up previous alleged work.

More On This...

The Parchin complex has been often mentioned in the West as a suspected base for secret nuclear experiments -- a claim Iran consistently denies. IAEA inspectors visited the site in 2005, but only one of four areas on the grounds and reported no unusual activities.

Last year, IAEA's report said there were indications Tehran has conducted high-explosives testing to set off a nuclear charge at Parchin. Iran denied the atomic activity and insisted that any decision to open the site rests with the armed forces since it was a military, not nuclear, facility.

Speaking Monday in Vienna, Austria, Amano said the suspicions of "activities ... ongoing at the Parchin site" in Iran means "going there sooner is better than later" for IAEA inspectors seeking to probe suspicions that Iran has been -- or is -- working secretly to develop nuclear arms.

"We have our credible information that indicates that Iran engaged in activities relevant to the development of nuclear explosive devices," Amano said told reporters outside of a 35-nation IAEA board meeting in Vienna, describing his sources as "old information and new information."

Iran denies any intention of possessing nuclear weapons and says all of its atomic activities are peaceful, but the IAEA says it has intelligence-based suspicions that may not be the case, based on thousands of pages of documentation.

Tehran has dismissed the information, saying it was based on "fabricated documents" provided by a "few arrogant countries" -- a phrase authorities often use to refer to U.S. and its allies.

"Given that Parchin is a military site, access to this facility is a time-consuming process and it can't be visited repeatedly," ISNA quoted the Iranian statement as saying. It added that following repeated IAEA demands, "permission will be granted for access once more."

The statement added that Tehran and IAEA need to agree on "modalities" before the visit can take place.

There was no immediate comment at the IAEA headquarters in Vienna on Tehran's decision. It comes as fears are growing that Israel's air force may soon strike Iran in an attempt to destroy its nuclear facilities.

During the IAEA visit last month, Iran invited the U.N. inspectors to visit Marivan site -- an offer they declined.

Amano's report last November also mentioned Marivan, saying that intelligence from an IAEA member state indicated large scale high explosive experiments were conducted in the western region of Marivan, near the Iraqi border.

Amano said Monday that Iran had made a last-minute offer to IAEA to visit Marivan. "With that we can't do a serious job. That's why we didn't go to Marivan."

President Barack Obama met with Benjamin Netanyahu in Washington on Monday and told the Israeli prime minister that the United States "will always have Israel's back," but that diplomacy is the best way to resolve the crisis over potential Iranian nuclear weapons.