UNITED NATIONS — Iran is not cooperating with an investigation into suspected secret work on nuclear weapons, the U.N. nuclear chief said Monday.

Yukio Amano told the U.N. General Assembly that talks between the Vienna-based International Atomic Energy Agency and Iran have intensified this year after an agency report in November 2011 said it had “credible information that Iran had carried out activities relevant to the development of a nuclear explosive device,” he said.

“However, no concrete results have been achieved so far,” Amano said.

While the atomic energy agency continues to verify that Iran’s declared nuclear material is not being diverted from peaceful purposes, “Iran is not providing the necessary cooperation to enable us to provide credible assurance about the absence of undeclared nuclear material and activities,” Amano said.

“Therefore, we cannot conclude that all nuclear material in Iran is in peaceful activities,” he said.

But the agency directorgeneral said, “The agency is firmly committed to intensifying dialogue with Iran.”

“We will continue negotiations with Iran on a structured approach,” he said. “I hope we can reach agreement without further delay.”

Iran has repeatedly denied any interest in possessing nuclear arms, but the international community fears that Tehran may turn its peaceful uraniumenrichment program toward the manufacture of weapons - a concern that is growing as the government expands the number of machines it uses to enrich its stockpile of enricheduranium.

As those fears grow, so does concern that Israel could carry out its threats to attack Iran’s nuclear facilities before that nation reaches the bomb-making threshold.

Iran’s U.N. Ambassador Mohammad Khazaee reiterated his country’s position thatit has a right to develop nuclear energy for peaceful purposes and rejected the claims in the International Atomic Energy Agency report saying they are “not credible” and based on “forged reports” provided by Israel and the United States.

Israeli Prime Minister Benjamin Netanyahu pledged on Israeli TV that as long as he is prime minister, Iran will not go nuclear.

“We are serious,” he said. “This is not a show. If there is no other way to stop Iran, Israel is ready to act.”

In his annual report to the world body, Amano said he also remains “seriously concerned” about North Korea’s nuclear program, calling its statements about uranium-enrichment activities and the construction of a light-water reactor “deeplytroubling.”

In late 2010, Pyongyang unveiled a uranium-enrichment facility that could give North Korea a second route to manufacture nuclear weapons in addition to its plutonium-based program. Earlier this year, satellite images showed thatNorth Korea has made progress in building a light-water reactor to expand its nuclear program.

North Korea is under tough U.N. sanctions, and Amano called on Pyongyang to comply with its obligations under Security Council resolutions and the Nuclear Nonproliferation Treaty and “to cooperate promptly and fully” with the International Atomic Energy Agency.

North Korea’s deputy U.N. ambassador Ri Tong Il rejected Amano’s report, saying the country is not a party to the treaty or a member of the International Atomic Energy Agency because the agency is not impartial and has “blindly” sided with the United States.

“Now, if you look at the current situation and developments on the Korean peninsula, the United States did not hesitate to escalate, aggravate, increase its threats and blackmails with increased hostilities toward the DPRK,” he said, using the initials of the country’s official name, the DemocraticPeople’s Republic of Korea.

“And the situation on the peninsula is on the brink of explosion, and nobody knows when the war will break out,” Ri warned.

Under this situation, he said, six-party talks on the North’s nuclear disarmament, which Pyongyang walked away from in 2009, have come “to the point of becoming almost a dead body at the moment.” The talks include the U.S., China, Japan, Russia, North and South Korea.

Ri said North Korea is a fullfledged nuclear weapon state and should be treated the same way as other nuclear weapon states like the United States, whose activities are not investigated by the International Atomic Energy Agency.

Amano also urged the Syrian government to respond to questions about a building destroyed by Israeli warplanes at the Deir El-Zour site in the Syrian desert in 2007. The International Atomic Energy Agency has said the building was “very likely” the covert site of a nuclear reactor.

Front Section, Pages 5 on 11/06/2012