Officials from the UN nuclear watchdog and Iran hold a fresh round of talks on August 24 on Teheran's controversial nuclear program.
The talks in Vienna at the headquarters of the International Atomic Energy Agency come amid fresh suspicions over Iran's nuclear program.
Western diplomats say Iran has installed many more uranium enrichment machines at its Fordow facility, despite UN sanctions punishing Iran for failing to curb its enrichment activities.
Western diplomats also claim Iran is cleaning up facilities at its Parchin site, allegedly to remove any sign of illicit nuclear activity.
There was no immediate comment from Iran's mission to the IAEA to the fresh claims.
In the past, Tehran has dismissed allegations about Parchin, which it says is a normal military site.
The IAEA suspects Iran has conducted tests with a military dimension at Parchin and at the talks IAEA officials are expected to again press Iran for access to Parchin.
Iran has long denied it is developing nuclear weapons, a charge leveled by many Western countries.
The fresh round of talks follow discussions that ended in failure in June.
The IAEA negotiations are separate from talks between Iran and world powers that have made little progress since restarting in April after a 15-month hiatus.
Analysts say the talks come at a crucial time with several Israeli senior officials suggesting Israel might attack Iran ahead of the U.S. presidential election in November.
Commentators say a lack of progress in negotiations with Iran over its nuclear program could further cement Israel's belief that tougher Western sanctions are failing to sway Tehran.
Meanwhile, the AP news agency reports the IAEA is forming a special Iran team, composed of experts in weapons technology, intelligence analysis, radiation and other fields.
Diplomats likened the IAEA's planned Iranian team to the agency's Iraq "Action Team," which uncovered parts of Saddam Hussein's nascent nuclear-weapons program in the 1990s.
Based on AP and Reuters reporting