Extensive construction activities at Iran's Parchin military base may have removed all evidence of alleged nuclear weapons research, the head of the UN atomic agency said Monday.

"As our verification capacity has been negatively impacted by extensive activities (at Parchin), it may no longer be possible to find anything even if we are given access," Yukiya Amano of the International Atomic Energy Agency told reporters in Vienna.

He said however that agency inspectors still wanted to visit the base near Tehran despite what he called the massive removal of soil, asphalting and possible dismantling of infrastructure.

The IAEA believes Iran installed a large explosives containment vessel at Parchin to conduct experiments that it says would be "strong indicators of possible nuclear weapon development".

Iran denies ever having worked on developing a nuclear weapon, and says that the IAEA's allegations are based on faulty intelligence provided by its enemies.

(AFP)