VIENNA (AP) — The U.N. atomic agency has received new and significant intelligence over the past month that Iran has moved further toward the ability to build a nuclear weapon, diplomats tell The Associated Press.

They say the intelligence shows that Iran has advanced its work on calculating the destructive power of an atomic warhead through a series of computer models that it ran sometime within the past three years.

The diplomats say the information comes from Israel, the United States and at least two other Western countries and concludes that the work was done sometime within the past three years. The time-frame is significant because if the International Atomic Energy Agency decides that the intelligence is credible, it would strengthen its concerns that Iran has continued weapons work into the recent past — and may be continuing to do so.

Because computer modeling work is normally accompanied by physical tests of the components that go into a nuclear weapons, it would also buttress IAEA fears outlined in detail in November that Tehran is advancing its weapons research on multiple fronts.

"You want to have a theoretical understanding of the working of a nuclear weapon that is then related to the experiments you do on the various components," said David Albright, whose Washington-based Institute for Science and International Security is a frequent go-to source on Iran for Congress and other U.S. government branches. "The two go hand-in-hand."

Such computer mock-ups typically assess how high explosives compress fissile warhead material, setting off the chain reaction that results in a nuclear explosion. The yield is normally calculated in kilotons.

Any new evidence of Iranian research into nuclear weapons is likely to strengthen the hand of hawks in Israel who advocate a military strike on Iran. They argue that Tehran is deliberately stalemating international efforts at engagement while continuing its clandestine weapons work.

Iran denies any interest in nuclear weapons and says suspicions that it ever tried to develop them are based on fabricated U.S, Israeli and other intelligence. At the same time, it has blunted IAEA efforts to investigate such claims for more than five years.

It also has scoffed at Western allegations that it is enriching uranium to make the core of nuclear warheads, saying it seeks only to create reactor fuel. But it refuses to accept offers of such fuel from abroad and is now producing material that is easier to turn into weapons-grade uranium than its main, lower-enriched stockpile.

The revelations come as Israeli officials are expressing growing alarm over what they see as continuing Iranian progress toward nuclear arms.

Israeli Prime Minister Benjamin Netanyahu engaged this week in a strident public exchange with the U.S. administration, calling on Sunday for "red lines" to be set for Iran. The calls were rebuffed, and on Tuesday, Netanyahu declared that "those in the international community who refuse to draw a red line on Iran don't have a moral right to place a red light before Israel."

Netanyahu said that sanctions were hurting Iran's economy but not nearly enough to compel it to stop the nuclear program, and said negotiations by the international community with Iran on the issue had failed.

Israel's position is that airtight sanctions are needed against Iran's central bank and oil exports. Because Asian nations in particular keep buying Iranian oil the country remains a top OPEC oil exporter, even though there are signs that its revenues are down and, with the currency plummeting, standards of living in Iran have fallen.

The comments from Netanyahu were the latest suggestion that Israel is considering taking military action on its own to at least slow down Iran's program. That prospect could badly rattle world markets and spark wider war, and is opposed not only in most Western capitals but also among many in Israel's security and political establishment. But Israeli officials have said that with Iran moving facilities underground its window of opportunity is closing while the world dithers with an inadequate sanctions regime.

Although some of the new information was said to have been supplied by the United States, it appears to run counter to the stated U.S. position that Iran shut down wide-ranging secret research and development of the components of a nuclear weapons program in 2003. At the same time the U.S. fears that Iran continues to move toward the threshold of making such arms by enriching uranium.

Ali Asghar Soltanieh, Iran's chief IAEA delegate, cut short a telephone request for comment, saying he could not talk because he was in a meeting. In Tehran, meanwhile, Foreign Ministry spokesman Rahmin Mehmanparast told reporters that Iran will start answering the agency's "questions and concerns" only when "our rights and security issues" are recognized.

IAEA spokeswoman Gill Tudor said the agency would not comment. But four of six diplomats who spoke to the AP on the issue said an oblique passage in the IAEA's August Iran report saying "the agency has obtained more information which further corroborates" its suspicions alludes to the new intelligence.

All six demanded anonymity because they were not authorized to discuss classified information member countries make available to the IAEA.

Two of them said the new information builds on what the agency previously knew, not only because the research was apparently performed past 2009 but also because it reflects that Iran has allegedly moved closer to the overall ability to develop a nuclear weapon.

The IAEA first outlined suspicions in November that Iran was working on calculating the yield of a nuclear weapon, as part of a 13-page summary of Iran's suspected nuclear weapons work that it said was based on more than 1,000 pages of research and intelligence from more than 10 member nations.

It said then that "the modeling studies alleged to have been conducted in 2008 and 2009 by Iran ... (are) of particular concern," adding that the purpose of such studies for calculating anything other than nuclear explosion yields is "unclear to the agency."

Albright, of the Institute for Science and International Security, said such computer-run modeling is "critical to the development of a nuclear weapon."

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George Jahn can be reached at http://twitter.com/georgejahn

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Associated Press writers Dan Perry in Jerusalem and Nasser Karimi in Tehran contributed.

The U.S. Consulate in Benghazi is seen in flames during a protest by an armed group said to have been protesting a film being produced in the United States September 11, 2012. An American staff member of the U.S. consulate in the eastern Libyan city of Benghazi has died following fierce clashes at the compound, Libyan security sources said on Wednesday. Armed gunmen attacked the compound on Tuesday evening, clashing with Libyan security forces before the latter withdrew as they came under heavy fire. REUTERS/Esam Al-Fetori

BEIRUT (Reuters) - The U.S. ambassador to Libya and three otherembassy staff were killed in a rocket attack on Tuesday night that targeted his car in the eastern Libyan city of Benghazi, a Libyan official said on Wednesday.

"The American ambassador and three staff members were killed when gunmen fired rockets at them," the official in Benghazi told Reuters. Asked about the deaths, a U.S. Embassy employee in Tripoli said: "We have no information regarding this." The employee said the embassy could confirm the death of one person.

The Libyan official said the U.S. ambassador had been on his way to a safer venue after protesters attacked the U.S. Consulate in Benghazi and opened fire, killing a staff member, in protest at a U.S. film that they deemed blasphemous to the Prophet Mohammad.

The official said the ambassador and three other staff were killed when gunmen fired rockets at his car. He said the U.S. Embassy had sent a military plane to transport the bodies to Tripoli to fly them to the United States.

Gunmen assaulted the Benghazi compound on Tuesday evening, clashing with Libyan security forces, who withdrew under heavy fire. The attackers fired at the buildings while others threw handmade bombs into the compound, setting off small explosions. Small fires were burning around the compound.

The assault followed a protest in neighboring Egypt where demonstrators scaled the walls of the U.S. embassy, tore down the American flag and burned it during a protest over the same film which they said insulted the Prophet Mohammad.

(Reporting by Samia Nakhoul and Marie-Louise Gumuchian; Editing by Mark Heinrich)