The UN nuclear watchdog has said its independence is paramount and it does not take intelligence presented to it at face value, in an apparent response to Israeli Prime Minister Benjamin Netanyahu's claims of a "secret atomic warehouse" in Iran.

Netanyahu - who opposes the nuclear deal between Iran and major powers that the International Atomic Energy Agency is policing - made the claim in a speech to the United Nations General Assembly last week. He urged the IAEA to visit the site in Tehran. A U.S. State Department official later seconded that call.

"The agency sends inspectors to sites and locations only when needed. The agency uses all safeguards relevant to information available to it but it does not take any information at face value," IAEA chief Yukiya Amano said in a statement on Tuesday, Reuters reported.

Amano's statement made no specific reference to Israel but it is his first public pronouncement since Netanyahu's speech. He said the IAEA has carried out so-called complementary access inspections, which are often at short notice, at all locations in Iran it has needed to visit.

"All information obtained, including from third parties, is subject to rigorous review and assessed together with other available information to arrive at an independent assessment based on the agency's own expertise," Amano said.

"In order to maintain credibility, the agency's independence in relation to the implementation of verification activities is of paramount importance," he added.