VIENNA (AP) — The head of the UN nuclear agency expressed frustration with Iran’s refusal to cooperate with a probe of what he suspects could be secret work on nuclear weapons, saying long-denied access to one particular site is necessary “without delay.”

Yukiya Amano also said that his International Atomic Energy Agency cannot vouch for Tehran’s assertion that all of its nuclear activities are peaceful unless it starts to cooperate with agency experts looking into information that suggests otherwise.

Amano spoke Monday to the 35-nation IAEA board. He singled out a site at Parchin, southeast of Tehran, as of particular interest. His experts have tried — and failed — since February to get access to buildings there thought to have been used for secret weapons work.

Copyright 2012 The Associated Press.