Gunmen Assassinate Iran’s Top Nuclear Scientist in Ambush, Provoking New Crisis - The New York Times

Iran expressed fury over the killing of Mohsen Fakhrizadeh, blaming it on Israel and the United States.

His death may complicate President-elect Biden’s intention to restore the Iranian nuclear deal.

Iran’s top nuclear scientist, long identified by American and Israeli intelligence as the guiding figure behind a covert effort to design an atomic warhead, was shot and killed Friday in what Iranian media called a roadside ambush as he and his bodyguards traveled outside Tehran.

For two decades, the scientist, Mohsen Fakhrizadeh, was the driving force behind what American and Israel officials describe as Iran’s secretive nuclear weapons program.

And his work continued after Iran’s push to develop a bomb was formally disbanded in 2003, according to American intelligence assessments and Iranian nuclear documents stolen by Israel nearly three years ago.

One American official — along with two other intelligence officials — said that Israel was behind the attack on the scientist.

It was unclear how much the United States may have known about the operation in advance, but the two nations are the closest of allies and have long shared intelligence regarding Iran, which Israel considers its most potent threat.

Iranian officials, who have always maintained that their nuclear ambitions are for peaceful purposes, not weapons, expressed fury and vowed revenge over the assassination, calling it an act of terrorism and warmongering that they quickly blamed on Israeli assassins and the United States.

Fakhrizadeh’s assassination — only 10 months after the United States killed the powerful spymaster at the head of Iran’s security machinery in a drone attack in Iraq — could greatly complicate President-elect Joseph R.

Biden Jr.’s plans to reactivate the 2015 nuclear agreement between Tehran and six other nations, which curtailed Iran’s nuclear activities.

President Trump withdrew the United States from the nuclear accord in 2018, unraveling the signature foreign policy achievement of his predecessor, Barack Obama, and isolating the United States from Western allies who tried to keep the agreement intact.

Since then, Iran has begun to increase its nuclear capacities once again, arguing that it is not bound by the nuclear accord because the United States reneged on its commitments.

“Terrorists murdered an eminent Iranian scientist today,” Iran’s foreign minister, Mohammad Javad Zarif, wrote on Twitter.

Zarif, who negotiated the Iran nuclear deal and remains one of Iran’s most recognizable figures, said in the post that the international community should “end their shameful double standards & condemn this act of state terror.”.

But some American officials argued that the death of Mr.

Fakhrizadeh comes just two weeks after intelligence officials confirmed that Al Qaeda’s second-highest leader was gunned down on the streets of Tehran by Israeli assassins on a motorcycle on Aug.

7, at the behest of the United States.

Iran never agreed to demands from the International Atomic Energy Agency, the United Nations’ nuclear monitor, to let U.N.

In 2008, his name was added to a list of Iranian officials whose assets were ordered frozen by the United States.

But an Israeli operation in early 2018 that stole a warehouse full of Iranian documents about “Project Amad,” what the Iranians called the nuclear weapons effort 20 years ago, included documents about Mr.

Israeli officials, later backed up by American intelligence officials who reviewed the archive, said the scientist had kept elements of the program alive even after it was ostensibly abandoned.

Milley, the chairman of the Joint Chiefs of Staff — argued against a military strike against Iran, top American officials and commanders still warn of what they call Iran’s malign activities

In Iran, some officials and commentators acknowledged that Mr