The head of the United Nations' nuclear monitoring agency has urged Iran to allow international monitors “early access” to a military site at the center of a long-stalled probe into Tehran's controversial nuclear program.

The comments of IAEA chief Yukiya Amano come after satellite images made public in recent days indicate Iran has been demolishing buildings at the military site known as Parchin.

Amano said he is aware of those images, he says, making it more urgent that inspectors visit the base where the West believes Iran has been conducting preliminary activities toward the development of a nuclear weapon.

The IAEA and Iran have been negotiating over the access issue in the last weeks. Amano, who traveled last month to Tehran, said another meeting between the agency and the Iranian government is scheduled for June 8.

The Iranian government says its program is for peaceful civilian nuclear energy research, but Western nations and Israel suspect it is for weapons.

A U.S. research organization said last week that the recent satellite images suggest Iran may be trying to wipe traces of nuclear weapon testing from Parchin.

The Washington-based Institute for Science and International Security said the images showed evidence “two small buildings at the same site as the suspected testing chamber have been razed.”

The ISIS report also said “heavy machinery tracks and extensive evidence of earth displacement” can be seen throughout the site.

ISIS says the satellite images were taken May 25 and support other images from April that indicated Iran had begun clean-up activities at the Parchin site. It also says the new images “raise further concerns of Iranian efforts to destroy evidence of alleged past nuclear weaponization activities.”

World powers agreed with Iran at a meeting last month to hold more talks on the nuclear issue starting June 18. Iran's delegation to last month's meeting in Baghdad claimed it offered its own proposal for ending the dispute.

Iranian state media said the delegation received no response to its offer.

Western powers fear Iran could quickly upgrade its uranium to the 90 percent purity needed for nuclear weapons. Iran wants an easing of international sanctions in return for any concession on enrichment work, which it says is meant for medical research and generating electricity.