Investigators at Tughlaq Road police station inspect a vehicle that exploded near the Israeli embassy in New Delhi, on February 14, 2012. The blast that badly wounded an Israeli diplomat was a terrorist attack by a highly-trained operative, the Indian government said, as Israel accused Iran of being responsible. (Prakash Singh/AFP/Getty Images)

In November, the tide of daily cable traffic to the U.S. Embassy in Azerbaijan brought a chilling message for Ambassador Matthew Bryza, then the top U.S. diplomat to the small Central Asian country. A plot to kill Americans had been uncovered, the message read, and embassy officials were on the target list.

The details, scant at first, became clearer as intelligence agencies from both countries stepped up their probe. The plot had two strands, U.S. officials learned, one involving snipers with silencer-equipped rifles and the other a car bomb, apparently intended to kill embassy employees or members of their families.

Both strands could be traced back to the same place, the officials were told: Azerbaijan’s southern neighbor, Iran.

The threat, many details of which were never made public, appeared to recede after Azerbaijani authorities rounded up nearly two dozen people in waves of arrests early this year. Precisely who ordered the hits, and why, was never conclusively determined. But U.S. and Middle Eastern officials now see the attempts as part of a broader campaign by Iran-linked operatives to kill foreign diplomats in at least seven countries over a span of 13 months. The targets have included two Saudi officials, a half-dozen Israelis and — in the Azerbaijan case — several Americans, the officials say.

In recent weeks, investigators working in four countries have amassed new evidence tying the disparate assassination attempts to one another and linking all of them to either Iran-backed Hezbollah militants or operatives based inside Iran, according to U.S. and Middle Eastern security officials. An official report last month summarizing the evidence cited phone records, forensic tests, coordinated travel arrangements and even cellphone SIM cards purchased in Iran and used by several of the would-be assailants, said two officials who have seen the six-page document.

Strikingly, the officials noted, the attempts halted abruptly in early spring, at a time when Iran began to shift its tone after weeks of bellicose anti-Western rhetoric and threats to shut down vital shipping lanes. In March, Iranian officials formally accepted a proposal to resume negotiations with six world powers on proposals to curb its nuclear program.

“There appears to have been a deliberate attempt to calm things down ahead of the talks,” said a Western diplomat briefed on the assassination plots, who spoke on the condition of anonymity because of the sensitivity of the intelligence. “What happens if the talks fail — that’s anyone’s guess.”

Less clear is whether the attempts were ordered by government officials or perhaps carried out with the authorities’ tacit approval by intelligence operatives or a proxy group such as Hezbollah. Many U.S. officials and Middle East experts see the incidents as part of an ongoing shadow war, a multi-sided, covert struggle in which Iran also has been the victim of assassinations. Four scientists tied to Iran’s nuclear program have been killed by unknown assailants in the past three years, and the country’s nuclear sites have been hobbled by cyberattacks. Iran has accused the United States and Israel of killing its scientists, but it has repeatedly denied any role in plots to assassinate foreign diplomats abroad.

The Obama administration has declined to directly link the Azerbaijan plot to the Iranian government, avoiding what could be an explosive accusation at a time when the two governments are engaged in negotiations on limiting Iran’s nuclear program. U.S. officials say they are less convinced that top Iranian and Hezbollah leaders worked together to coordinate the attempted hits, noting that both groups have a long history of committing such acts on their own, and for their own purposes.

“The idea that Iran and Hezbollah might have worked together on these attempts is possible,” said a senior U.S. official who has studied the evidence, “but this conclusion is not definitive.”

‘Walking a fine line’

Attacks directly targeting American diplomats are rare but not unknown. In 2002, Laurence Foley, a senior official at the U.S. Embassy in Jordan, was fatally shot by suspected Islamist extremists outside his home in Amman, and other diplomats have been killed in recent years in Pakistan, Sudan and Iraq. U.S. intelligence officials believe that Americans would probably have been killed if an alleged Iranian plot to kill Saudi Arabia’s ambassador to Washington last year had succeeded.

In Azerbaijan, however, embassy officials have been alerted to plots against employees at least three times in the past two years. In each case, the alleged planners were discovered and the threats quietly put down by Azerbaijani authorities, working closely with American counterterrorism officials, according to U.S. and Middle Eastern officials familiar with the incidents. Azerbaijan, a majority-Muslim country of 9 million, has had a troubled history with its much larger neighbor to the south, but it publicly seeks to maintain friendly relations with Iran, whose population is 16 percent ethnic Azerbaijani.

Embassy employees were told little about the threats. Bryza, the ambassador at the time, worked with embassy security officers to quietly tighten procedures while officials in Washington tried to assess the seriousness of the threats, the officials said. Bryza, who left the State Department this year after the Senate blocked confirmation of his re-nomination to the ambassador’s post, declined to comment about the events.

“They were walking a fine line, trying to avoid panic while taking the necessary precautions,” said a former State Department official who dealt regularly with the embassy. “There was a constant operational concern during that time.”

The most recent threat came to light after a foreign spy agency intercepted electronic messages that appeared to describe plans to move weapons and explosives from Iran into Azerbaijan. Some of the messages were traced to an Azerbaijani national named Balagardash Dashdev, a man with an extensive criminal background and, according to a Middle East investigator involved in the case, deep ties to a network of intelligence operatives and militant groups based inside Iran.

Working from inside Iran, officials said, Dashdev in late October began coordinating the shipment of explosives, weapons and cash to Azerbaijani contacts, including relatives and former criminal associates. As U.S. and Middle Eastern intelligence deepened their surveillance, they began to discern what the Middle Eastern investigator described as a “jumble of overlapping plans,” some specifically aimed at Azerbaijan’s small Jewish community and others targeting diplomats and foreign-owned businesses in Baku, the country’s sprawling capital on the Caspian Sea.

During the late fall and early winter, the weapons were smuggled into the country along with at least 10 Iranian nationals recruited to help carry out the plot, U.S. and Middle Eastern officials said.

The Azerbaijani participants had been paid a cash advance and were beginning to conduct surveillance on a list of targets — including a Jewish elementary school, a U.S.-owned fast-food restaurant, an oil company office and “other objects in Baku,” according to a brief statement issued by the Azerbaijani government after a series of raids in which about two dozen alleged accomplices were arrested between January and early March.

The Obama administration acknowledged in March that the U.S. Embassy may have been among the intended targets. But in the months since then, the suspects under questioning revealed extensive details about the “other objects in Baku” that had been on the target list, confirming that the would-be assassins intended to go beyond attacks on buildings.

“They were going after individuals,” said the former State Department official who worked closely with the embassy in Baku. “They had names [of employees]. And they were interested in family members, too.”

The alleged plot leader, Dashdev, would tell investigators that the planned attacks were intended as revenge for the deaths of the Iranian nuclear scientists, attacks that Iran has publicly linked to Israel and the United States. Iran vehemently denied involvement in any assassination plot inside Azerbaijan, and the Iranian Embassy in Baku suggested in a statement that the plot was fiction.

“We believe that the glorious people of Azerbaijan understand that this part of the script of Iranophobia and Islamophobia is organized by the Zionists and the United States,” the statement read. Attempts to contact Iranian officials for additional comments for this article were unsuccessful. Dashdev, who confessed to his role in a videotaped message broadcast on Azerbaijani television, remains in custody and could not be reached for comment. Baku officials have repeatedly accused Iran of stirring up unrest among pro-Iranian extremists to drive a wedge between Azerbaijan’s population and its government, which cooperates closely and openly with Western counterterrorism agencies.

“What we are trying to do is build a strong, independent nation that is a responsible actor,” Elin Suleymanov, Azerbaijan’s ambassador to Washington, said in an interview. “We have told all our friends and neighbors that expressing disagreement in a civilized way is more beneficial than resorting to terrorism or promoting radicalization.”

String of foiled attacks

U.S. and Middle Eastern officials say the Azerbaijan plot fits a pattern seen in numerous other recent attempts linked to Iran. The foiled assassination of Saudi Arabia’s ambassador to Washington involved a similar plan to hire criminal gangs — in this case, members of a Mexican drug cartel — to kill a senior diplomat in a public setting, U.S. intelligence officials note.

The report presented to U.S. officials last month asserts extensive links between attempted assassinations of diplomats in five other countries: India, Turkey, Thailand, Pakistan and the former Soviet republic of Georgia. Each attempt was carried out by operatives with direct ties to Iran or Hezbollah and directed against diplomats from countries hostile to Iran, the reports states.

Israeli and Indian officials have described substantial Iranian links to a car bombing in February that seriously wounded the wife of an Israeli diplomat in New Delhi. In that Feb. 13 attack, an assailant on a motorcycle attached a magnet bomb to a diplomatic car in which the woman was riding, injuring her and her driver. Indian police have charged an Indian man — a free-lance journalist working for Iranian news organizations — with organizing the attack with the help of three Iranian nationals who had entered the country.

The next day, an alleged plot to kill Israeli diplomats in Bangkok was thwarted when a bomb being assembled exploded prematurely.

The car bombs prepared for use in both attacks were virtually identical, with a magnetic outer shell that was smuggled into the two countries, to be combined later with C4 military explosives obtained from a still-unknown source. Two of the Iranian nationals allegedly involved in the Bangkok attempt were captured, and they, like the suspects in Azerbaijan, are continuing to provide clues to investigators.

The suspects, thought to be low-level operatives, either do not know or will not say who ordered the attacks, leaving investigators to speculate about how far up within Iran’s government the plots may have originated.

“There is not yet a smoking gun,” said the Western diplomat briefed on the evidence. “But the pattern is clear, and each day the volume of evidence grows.”