United Nations inspectors will be present with Iranian technicians as they take samples from a key military site, two Western diplomats said, undercutting an objection by U.S. Republicans to the nuclear deal between Iran and world powers.

The diplomats were familiar with details of a confidential arrangement between Iran and the U.N. nuclear watchdog for inspections at the Parchin site, where some countries suspect nuclear weapons-related tests may have taken place.

Iran has denied that allegation, but agreed to accept comprehensive International Atomic Energy Agency (IAEA) inspections of its suspect sites as part of the historic July deal in exchange for an easing of international sanctions.