The Trump administration for the first time formally blamed Iran for the presumed death of retired FBI agent Robert Levinson, publicly identifying two Iranian intelligence officers believed responsible for his abduction.

Mr Levinson disappeared in Iran under mysterious circumstances more than a decade ago, and though US diplomats and investigators have long said they thought he was taken by Iranian government agents, Monday’s announcement in the final weeks of the Trump administration was the most definitive assignment of blame to date.

Besides blaming two high-ranking intelligence officers by name, US officials said the Iranian regime sanctioned the plot that led to Mr Levinson’s abduction and lied for years about its involvement in his disappearance through disinformation campaigns aimed at covering up the government’s role.

The announcement comes nine months after US officials revealed that they had concluded that Mr Levinson “may have passed some time ago” though they did not disclose at the time the information that led them to that assessment.

Officials on Monday would not describe any additional information that led them to believe Mr Levinson had died in captivity, except to say that all evidence they had pointed in that direction, or how they came to identify the role of the two individual intelligence officers.

Officials said they were acting now, one month before President Donald Trump leaves office, not for any political reasons but simply because they had finally accumulated enough information to formally hold Iran accountable.

They also said that no agreement with Iran should be reached without a deal to free the remaining handful of US citizens imprisoned in that country.

Mr Levinson vanished on March 9 2007, when he was scheduled to meet a source on the Iranian island of Kish.

For years, US officials would say only that Mr Levinson was working independently on a private investigation.

But a 2013 Associated Press investigation revealed that Mr Levinson had been sent on a mission by CIA analysts who had no authority to run such an operation.

The family received a video in late 2010 as well as proof-of-life photographs in 2011 in which he appeared dishevelled with a long beard and wearing an orange prison jumpsuit like those given to detainees at the Guantanamo Bay prison.

Even then, his whereabouts and fate were not known, and the Iran government has persistently denied having any information about Mr Levinson.

Read more: Iran ordered to pay £1 billion to family of kidnapped FBI agent presumed dead

A US judge has ordered Iran to pay 1.45 billion dollars (£1.12 billion) to the family of a former FBI agent believed to have been kidnapped while on an unauthorised CIA mission.

Robert Levinson’s family and the US government now believe he died in the Iranian government’s custody, something long denied by Tehran, though officials have offered contradictory accounts about what happened to him on Kish Island.

Tensions remain high between the US and Iran amid US President Donald Trump’s pressure campaign over Tehran’s nuclear programme.

Though the US and Iran have not had diplomatic relations since the aftermath of the 1979 US Embassy hostage crisis in Tehran, America stills holds billions of dollars in frozen Iranian assets that could be used to pay Mr Levinson’s family.

In a ruling from Thursday, the US District Court in Washington found Iran owed Mr Levinson’s family 1.35 billion dollars (£1.05 billion) in punitive damages and 107 million dollars (£82 million) in compensatory damages for his kidnapping.

The court cited the case of Otto Warmbier, an American college student who died in 2017 shortly after being freed from captivity in North Korea, in deciding to award the massive amount of punitive damages to Mr Levinson’s family.

Judge Timothy Kelly said: “Iran’s conduct here is also unique, given that – astonishingly – it plucked a former FBI and DEA special agent from the face of the earth without warning, tortured him, held him captive for as long as 13 years, and to this day refuses to admit its responsibility.

“And his wife and children, and their spouses and children – while keeping Levinson’s memory alive – have had to proceed with their lives without knowing his exact fate. These are surely acts worthy of the gravest condemnation.”

Iranian state media and officials in Tehran did not immediately acknowledge the ruling in a case in which Iran offered no defence and Iran’s mission to the United Nations did not immediately respond to a request for comment on Tuesday.

In a statement, Mr Levinson’s family called the court’s award “the first step in the pursuit of justice”.

It said: “Until now, Iran has faced no consequences for its actions.

“Judge Kelly’s decision won’t bring Bob home, but we hope that it will serve as a warning against further hostage taking by Iran.”

Mr Levinson disappeared from Iran’s Kish Island on March 9, 2007.

For years, US officials would only say that Mr Levinson, a meticulous FBI investigator credited with busting Russian and Italian mobsters, was working for a private firm on his trip.

In December 2013, it was revealed Mr Levinson in fact had been on a mission for CIA analysts who had no authority to run spy operations.

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