Dozens of unexplained explosions hit the country’s gas pipelines. Iran’s first nuclear power plant suffered major equipment failures as technicians struggle to bring it online.

Has Iran just been unlucky? Probably not.

The chief of Iran’s Atomic Energy Organization, Fereidoun Abbasi, told journalists at a meeting in Vienna last week that the United States was supporting an Israeli assassination campaign against his scientists. His comments came almost a year after motorcyclists attached a bomb to the door of his car in Tehran. He and his wife barely escaped.

As for the three slayings, Iranian President Ahmadinejad told The Associated Press that the killers had been caught and confessed to being "trained in the occupied lands by the Zionists." He accused the International Atomic Energy Agency of being under U.S. control and said the watchdog agency had "illegally and unethically" released the names of Iran’s nuclear researchers, making them targets.

While Israel and Britain won’t discuss Iran’s charges, the U.S. has denied any role in the slayings.

"We condemn any assassination or attack on a person — on an innocent person," State Department spokeswoman Victoria Nuland said after the latest killing in July. "We were not involved."

Former U.S. officials point out that assassinations are outlawed by the U.S., which condones drone strikes against terrorists as acts of war against combatants.

Yet there is little doubt that the Obama administration is pursuing a program of high-tech sabotage to disrupt Tehran’s suspected weapons-related nuclear efforts.

"I have no doubt that the U.S. and other countries were behind industrial sabotage aimed at the program of concern," said Mark Fitzpatrick, a former State Department official who’s now at the International Institute for Strategic Studies in London.

Tehran said it is pursuing nuclear technology for peaceful purposes. International inspectors said Iran has refused to explain suspected weapons work since 2008. The U.S. and other countries accuse Iran of making all the necessary preparations to build a nuclear arsenal.

Publicly, the administration has pushed for tougher penalties and further diplomatic isolation to pressure Iran to abandon weapons-related work. At the same time, former officials said, the U.S. and its allies have ramped up covert actions aimed at slowing Iran’s nuclear progress toward a bomb.

Ex-officials said the U.S. has been careful to target only those facilities suspected of playing a role in weapons work.

One former senior intelligence official said that the U.S. considered a scheme to use a burst of electromagnetic energy to knock out power to one suspected Iranian weapons-related site but rejected the plan because of the risk of causing a widespread power outage. The former official would only speak about classified matters on condition of anonymity.

The suspected sabotage campaign is widely seen as an alternative to military confrontation with Iran, which some experts say could have disastrous consequences for the Middle East.

A 2010 U.S. diplomatic memorandum published by the anti-secrecy group WikiLeaks quoted a German government official as saying that a program of "covert sabotage" against Iran, including explosions, computer hacking and engineered accidents, "would be more effective than a military strike whose effects in the region could be devastating." The memo did not cite any specifics.

While the fact is rarely discussed, the U.S. may be the world’s leader in high-tech industrial sabotage.

According to an official CIA history, the Reagan administration was convinced that the Soviet Union was engaged in the wholesale theft of Western technological secrets. It arranged for the shipment of doctored computer chips, turbines and blueprints to the USSR that disrupted production at chemical plants and a tractor factory. When the KGB obtained plans for NASA’s Space Shuttle, the CIA said it made certain it was for a rejected design.

Thomas C. Reed, a member of the National Security Council in the Reagan administration, wrote in his 2004 book that during the Cold War the CIA tampered with the computer code embedded in Canadian components of a new trans-Siberian gas pipeline system. In 1982, a surge in pressure caused a three-megaton blast in the Siberian forest that was visible from space.

The U.S. doesn’t regard Iran as an innocent victim.

Washington has accused Tehran of sponsoring terrorist groups in Iraq, Syria and Lebanon, of sending arms to the Taliban in Afghanistan and aiding al-Qaida’s leadership in Pakistan. The U.S.-supported Iran Human Rights Documentation Center has said that Iranian intelligence agents have killed more than 160 expatriate political activists abroad.

"We’ve been in a contest with the Iranians now for 30 years, and this is just one phase of it," said James Lewis, a former State Department official and an expert on technology and security. "The Iranians do things that appeal to them, and they are noisy and physical and explosive."

The U.S., he said, has preferred quieter methods that leave few fingerprints. "If I was Iran, I would wonder if my stuff would work," Lewis said.

The U.S. and its allies have avoided discussing the suspected sabotage campaign publicly. At least until recently, Iran has seldom raised the issue and even then has provided few details.

For both sides, the most sensitive issue is the question of who is killing Iran’s nuclear scientists.

Reuel Marc Gerecht, a former CIA officer now at the Foundation for the Defense of Democracies think tank, said a faction within Iran’s government might have ordered the assassinations. He said one researcher supported Iran’s persecuted opposition, while the others may have been suspected of spying for the West.

Other former officials and diplomats said the killings appear to be an effort by Iran’s adversaries to disrupt its nuclear weapons-related work.

Several warned that targeted killings can backfire if they were to inspire surviving engineers and scientists to work harder, or if Iran were to retaliate by targeting Western scientists. They also questioned whether assassinating a few researchers could slow such a large program.

"If the state and progress of the Iranian nuclear program depends on what is walking around inside the heads of one or two key officials, then we’ve got a lot less to worry about this program than most of the discourse would lead us to believe," said Paul Pillar, a former CIA national intelligence officer for the Near East and South Asia.

Former officials and experts generally agree that the Stuxnet worm was an effort to sabotage Iran’s uranium enrichment centrifuges, which can be used to make fuel for reactors or weapons-usable material for atomic bombs. Western experts estimate that the malware destroyed 1,000 centrifuges at Iran’s Natanz plant last year.

Some former U.S. officials said that Israel’s Unit 8200, the Defense Force’s electronic intelligence service, probably led the development of Stuxnet, with the help of the U.S. and perhaps other nations. Others said they suspected the U.S. was the chief developer of what has been called the world’s first cyberweapon of mass destruction.

German Stuxnet expert Ralph Langner said in a speech this spring that such advanced software must have been created by what he called a cybersuperpower. "There is only one," said Langner. "And that is the United States."

Art Keller, a retired CIA officer who worked in the Middle East and South Asia, said Stuxnet’s self-destruct mechanism, its painstaking focus on a single target and other fail-safe features all suggest the program was screened by U.S. government lawyers concerned about limiting collateral damage.

"These are all the hallmarks of a U.S. covert action," he said.

Insiders are divided on whether the West has conducted sabotage operations against Iran’s oil and gas pipeline networks.

Fitzpatrick, the former State Department nonproliferation expert, said U.S. and U.N. penalties have cut off Iran’s supply of replacement parts and forced it to manufacture crude knockoffs that frequently fail. "Only in that sense can one say with certainty that the West is responsible" for the country’s refinery and pipeline blasts, he said.

The Bushehr nuclear power plant suffered a rash of equipment malfunctions over the past year, including the failure of one of the plant’s emergency cooling pumps and flaws found in two bearings on one of the plant’s huge turbines.

Former U.S. officials said that Iran’s agreement to buy fuel for Bushehr from Russia and to return the plutonium-bearing spent fuel back to Russia for reprocessing eased concerns the plant could be used as part of a nuclear weapons effort. They doubted there was any U.S. interest in disrupting its operations.

Russian engineer Alexander Bolgarov, who spent two years working on the Iranian plant, told the AP in an interview last month that Stuxnet had no effect on Bushehr.

Bolgarov said he saw no other evidence of sabotage, either. Instead, he blamed Bushehr’s construction problems and breakdowns on inexperienced workers, poor oversight and overlapping Russian and Iranian bureaucracies.

Sometimes an accident is just an accident, even in Iran.

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Associated Press writers Gary Peach in Latvia, Adam Goldman in Washington and George Jahn in Vienna contributed to this report.