WASHINGTON: Investigators working in four countries have amassed new evidence linking attempts to assassinate officials and businessmen to either Iran-backed Hezbollah or Iran-based operatives, The Washington Post reported Monday.

Citing unnamed US and Middle Eastern security officials, the newspaper said the evidence included phone records, forensic tests, coordinated travel arrangements and even cellphone SIM cards purchased in Iran and used by several of the would-be assailants. Last year, Azerbaijan uncovered a plot to kill US Embassy employees or members of their families.

But the plot was apparently just one of many. Iranian-backed operatives have been linked to attempts to kill foreign diplomats in at least seven countries over a span of 13 months, the paper said.

The targets have included two Saudi officials, a half-dozen Israelis and, in the Azerbaijan case, several Americans, according to the report.

Strikingly 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, The Post said.

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,” the paper quotes an unnamed Western diplomat as saying. “What happens if the talks fail, that’s anyone’s guess.”

It is unknown whether the attempts were ordered by Iranian government officials or carried out with the authorities’ tacit approval by a proxy group such as Hezbollah, The Post noted.

Many US 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, the report said.

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, the paper noted.