The NPT aims to stop the spread of nuclear weapons and requires members to open their nuclear facilities to inspection to verify they are being used for purely peaceful purposes.

Mr. Grossi acknowledged that under the NPT, Iran is permitted to veto individual inspectors it does not agree with.

Pointing to precedents like Iraq and Libya, Israel has long worried that potentially hostile neighbors could use civilian nuclear energy and other projects developed under the 1970 NPT as cover for clandestine bombmaking.

Israel, which is outside the voluntary NPT and has no nuclear energy, is widely believed to have atomic weaponry.

Leaving the NPT would free Iran to develop nuclear arms.