Iran said Tuesday it might drop its opposition to UN inspectors visiting a military base thought to be central to its suspected nuclear weapons drive, but Western diplomats were highly skeptical.

Iran's diplomatic mission to the UN nuclear watchdog in Vienna, the International Atomic Energy Agency, said that access to the Parchin site "would be granted" -- provided certain conditions were met.

"Considering the fact that it is a military site, granting access is a time-consuming process and cannot be permitted repeatedly," the Iranian embassy said in a statement entitled "Short Glance on Realities on the Ground."

Iran said it had requested that the IAEA "combine all related issues ... and then once more, access would be granted" and that the "process could be obviously started" once there is agreement on how to resolve all issues.

The IAEA said in November that it suspected Iran had carried out blast experiments to design a nuclear warhead in a bus-sized metal container at the sprawling Parchin base.

Iran has denied the accusations and has said that the IAEA visited the site in 2005 and found nothing, but inspectors did not examine the area where the explosives chamber was believed to be.

Tehran also says that it is under no obligation to allow IAEA access to the site because it is not part of its nuclear programme.

IAEA chief Yukiya Amano on Monday also appeared to allege that Iran was removing evidence at the base, saying "activities" spotted by satellite "makes us believe that going there sooner is better than later."

During two high-level visits to Tehran this year, one in January and another in February, the IAEA said it had requested access to Parchin but that the Iranians "did not grant permission."

Iran on Tuesday said that between the two trips it "was agreed" that the agency's request to visit Parchin would be "postponed" until after this week's IAEA board of governors meeting.

The IAEA declined to comment but Western envoys said the Iranian statement fell well short of offering a way out of the impasse, with one telling AFP the offer of access to Parchin looked like "too little, too late."

"It doesn't seem like the fulsome cooperation the IAEA needs. The value of a one-time, conditioned visit after Iran may well have been sanitizing the site is questionable," the diplomat said on condition of anonymity.

Iran is highly sensitive about allowing access to military sites following a huge explosion at the Bid Ganeh base on November 12 that killed 36 Revolutionary Guards including a key figure in Iran's ballistic missile programme.

Several nuclear scientists have also been assassinated in attacks blamed by Tehran on the United States and Israel, the latest being the 32-year-old deputy director of Iran's Natanz uranium enrichment facility in January.

Iran in November accused the IAEA of making its scientists targets for assassination by Mossad and the CIA, the Israeli and US secret services, by making public their names.

Amano revealed for the first time on Monday that Iran had offered "a few hours before departure" during the second visit access to another site, in Merivan in the northwest, but that the agency had declined.

Iran, which has been subjected to tighter sanctions since the November report, says its atomic programme is peaceful and that it does not want nuclear weapons. The standoff has stoked speculation of possible Israeli air strikes.