WASHINGTON — At an Iranian military base 30 miles west of Tehran, engineers were working on weapons that the armed-forces chief of staff had boasted could give Israel a "strong punch in the mouth."

But a huge explosion then ripped through the Revolutionary Guard Corps base Nov. 12, leveling most buildings. Government officials said 17 people were killed, including a founder of Iran's ballistic-missile program, Gen. Hassan Tehrani Moghaddam.

Iranian officials called the blast an accident. Perhaps it was.

Decades of international sanctions have left Iran struggling to obtain technology and spare parts for military programs and commercial industries, leading in some cases to dangerous working conditions.

However, many former U.S. intelligence officials and Iran experts believe the explosion — the most destructive of at least two dozen unexplained blasts in the past two years — was part of a covert effort by the United States, Israel and others to disable Iran's nuclear and missile programs. The goal, the experts say, is to derail Iran's quest for a nuclear-weapons capability and to stave off an Israeli or U.S. airstrike to eliminate or lessen the threat.

"It looks like the 21st century form of war," said Patrick Clawson, who directs the Iran Security Initiative at the Washington Institute for Near East Policy, a Washington think tank. "It does appear that there is a campaign of assassinations and cyber war, as well as the semi-acknowledged campaign of sabotage."

Or perhaps not. Such an operation would be highly classified, and those who might know aren't talking. The result is the latest national-security parlor game in Washington, D.C. — trying to figure out who, if anyone, is responsible for the incidents.

Israeli newspapers declared last week that Israel's war with Iran already had begun, but that the Jewish state, rather than launch airstrikes, had decided on a method of covert action in cooperation with other groups. Statements by current and former Israeli officials were being parsed for clues but did little to clarify the issue.

"There aren't many coincidences, and when there are so many events there is probably some sort of guiding hand, though perhaps it's the hand of God," said Israel's former head of internal security, Maj. Gen. Giora Eiland.

The United States and its allies for years have sought to hinder Iran's weapons programs by secretly supplying faulty parts, plans or software, former intelligence officials say. No proof of sabotage has emerged, but Iran's nuclear program clearly has hit obstacles that thwarted progress in recent years.

"We definitely are doing that," said Art Keller, a former CIA case officer who worked on Iran. "It's pretty much the stated mission of the [CIA's] counter-proliferation division to do what it takes to slow ... Iran's weapons-of-mass-destruction program."

Many Western experts are convinced U.S. and Israeli engineers secretly fed the Stuxnet computer worm into Iran's nuclear program in 2010. The virus reportedly caused uranium-enriching centrifuges to spin out of control and shatter. Neither the U.S. nor Israeli government acknowledged a role.

Nor did anyone claim responsibility after two senior nuclear physicists were killed, and a third wounded, by bombs attached to their cars or nearby motorcycles in January and November last year.

Militants waving pictures of one of the slain scientists stormed the British Embassy in Tehran last week, setting fires and causing extensive damage. Several European countries recalled envoys from Iran after the British government closed its embassy and expelled Iranian diplomats from London.

Like the deaths, the explosions have drawn special scrutiny in think tanks, where Iran watchers have tracked reports of unexplained blasts in Iranian gas pipelines, oil installations and military facilities.

Iranian news services reported three such explosions in a 24-hour period in October. The blasts killed two people. Another one was reported last week in Esfahan, Iran's third-largest city.

Some analysts suspect the CIA and Israel's intelligence agency, Mossad, are involved, with possible help from the MEK, a fringe Iranian group that the State Department lists as a terrorist organization, although it has many allies in Washington's foreign-policy establishment. Based in Iraq, the group is believed to have links to dissident networks inside Iran.

Iran claims to have arrested dozens of CIA informants in recent months, and U.S. officials acknowledge a handful of informants in Iran have been exposed. What they did, or where, is unknown. U.S. officials in October announced they had uncovered a bizarre Iranian plot to assassinate the Saudi ambassador in Washington.

Some analysts caution against assuming the CIA is orchestrating all the attacks in Iran, arguing it gives U.S. intelligence far too much credit. But that doesn't preclude U.S. support for allied spy services in Europe and the Middle East that also target Iran. Still, there is more speculation at this point than hard evidence.

A cyber expert who works closely with U.S. intelligence said he is convinced Israel alone launched the Stuxnet attack because U.S. government lawyers would not approve use of a computer virus that could spread far beyond the intended target, as Stuxnet apparently did. That caution, of course, presumes the lawyers knew the virus would spread, and that's unclear. The expert would not speak publicly about classified matters.

Whether White House officials would authorize the targeted killing of Iranian scientists is far from certain. An executive order signed by President Reagan in 1981 prohibits direct or indirect involvement in assassinations, although the term is not defined.

President Obama has authorized slayings of al-Qaida members and other militants, including at least one U.S. citizen in Yemen.

Some analysts claim the United States would not back a bombing campaign that has killed Iranian workers at oil refineries and other civilian sites. Such a campaign would amount to sponsoring terrorism, a charge regularly leveled at Iran.

"I do not believe that the U.S. has participated in either attacking scientists or physical attacks against Iranian nuclear facilities," said Greg Thielmann, a former State Department intelligence official who helped expose faulty intelligence cited by the George W. Bush administration before the 2003 invasion of Iraq. "Selling them bad parts, introducing malware — that does seem to me within the realm of what one might expect from U.S. intelligence activities."

Reuel Marc Gerecht, a former CIA operative who specialized on Iran, said he doesn't believe the CIA could mount a sophisticated covert campaign of sabotage inside Iran, where the United States has not had an embassy since 1979. Gerecht, however, long has urged the CIA to mount more aggressive operations against Iran.

"I just think trying to maintain and run a paramilitary covert-action group inside Iran is beyond America's covert capacity," he said.

Whatever the cause, headlines about unsolved killings, unexplained explosions and sinister computer viruses have rattled Iranians, especially those who work in the nuclear program, analysts said.

Perhaps that's the point.

"All these things have a profound effect," Clawson said. "You have to watch your back when you go to work. You're not certain what's going to happen when you turn on your computer. You're not certain whether you can you talk to your colleagues."

Information from McClatchy Newspapers is included in this report.