Iran’s supreme leader on Saturday vowed to retaliate with “definitive punishment” after the slaying of the country's leading nuclear scientist, with some officials blaming Israel for the apparent assassination.

The Israeli government, suspected of assassinating Iranian scientists a decade ago amid tensions over Tehran’s nuclear ambitions, has yet to comment on the killing Friday of Mohsen Fakhrizadeh.

IRANIAN SCIENTIST TIED TO NUCLEAR PROGRAM ASSASSINATED

The roadside attack, which bore the hallmarks of a carefully planned, military-style ambush, threatens to further escalate tensions between the United States and Iran in the waning days of President Trump’s term and creates new complications for President-elect Joe Biden.

Biden has suggested he might return to a deal brokered by the Obama administration to limit Iran's nuclear development, a pact from which Trump -- a staunch ally of Israeli Prime Minister Benjamin Netanyahu -- withdrew in favor of what his administration termed a "maximum pressure" campaign against Tehran.

On Saturday, the Pentagon announced that it has sent the USS Nimitz aircraft carrier back to the Middle East, citing the drawdown of U.S. forces in Iraq and Afghanistan. As a symbol of American military might, the carrier might also prove a deterrent to any aggression from Iran.

Iranian Supreme Leader Ayatollah Ali Khamenei, who called the slain man "the country's prominent and distinguished nuclear and defensive scientist," said Iran’s first priority was the “definitive punishment of the perpetrators and those who ordered it.” He did not elaborate.

Speaking at a meeting of his government’s coronavirus task force earlier Saturday, President Hassan Rouhani blamed Israel for the killing.

Rouhani said Fakhrizadeh’s death would not stop Iran's nuclear program, underscoring a statement by Khamenei. Iran’s civilian nuclear program has continued its experiments and now enriches uranium up to 4.5%, far below weapons-grade levels of 90%.

But analysts have said Fakhrizadeh is on par with Robert Oppenheimer, the scientist who led the Manhattan Project to develop the atomic bomb during World War II.

“We will respond to the assassination of Martyr Fakhrizadeh in a proper time,” Rouhani said. “The Iranian nation is smarter than falling into the trap of the Zionists. They are thinking to create chaos.”

Friday’s attack happened in Absard, a village just east of the capital that is a retreat for the Iranian elite. Iranian state television said an old truck with explosives hidden under a load of wood blew up near a sedan carrying Fakhrizadeh.

As Fakhrizadeh’s sedan stopped, at least five gunmen emerged and opened fire, the semiofficial Tasnim news agency said.

Fakhrizadeh died at a hospital after doctors and paramedics were unable to revive him. Others wounded included Fakhrizadeh’s bodyguards. Photos and video shared online showed a Nissan sedan with bullet holes in the windshield and blood pooled on the road.

Mohsen Fakhrizadeh, right, sits in a meeting with Supreme Leader Ayatollah Ali Khamenei in Tehran in January 2019. (Office of the Iranian Supreme Leader via AP)

Mohsen Fakhrizadeh, right, sits in a meeting with Supreme Leader Ayatollah Ali Khamenei in Tehran in January 2019. (Office of the Iranian Supreme Leader via AP)

The Pentagon announced the return of the Nimitz to the Middle East, an unusual move as the carrier already spent months in the region, hours after the slaying.

The attack comes just days before the 10-year anniversary of the killing of Iranian nuclear scientist Majid Shahriari, which Tehran also blamed on Israel. That and other targeted killings happened at the time that the so-called Stuxnet computer virus, believed to be an Israeli-American creation, destroyed Iranian centrifuges.

Those assaults occurred at the height of Western fears over Iran’s nuclear program.

While Tehran has long insisted its program is peaceful, Fakhrizadeh led Iran’s so-called AMAD program that Israel and the West have alleged was a military operation looking at the feasibility of building a nuclear weapon.

The International Atomic Energy Agency says that “structured program” ended in 2003.

IAEA inspectors monitor Iranian nuclear sites as part of the now-unraveling nuclear deal with world powers, which saw Tehran limit its enrichment of uranium in exchange for the lifting of economic sanctions.

After Trump’s 2018 withdrawal from the pact, Iran abandoned all those limits. Experts now believe Iran has enough low-enriched uranium to make at least two nuclear weapons if it chose to pursue a bomb. Meanwhile, an advanced centrifuge assembly plant at Iran’s Natanz nuclear facility exploded in July in what Tehran now calls a sabotage attack.

Fakhrizadeh, born in 1958, had been sanctioned by the U.N. Security Council and the U.S. for his work on AMAD. Iran always described him as a university physics professor. A member of the Revolutionary Guard, Fakhrizadeh had been seen in pictures of meetings attended by Ayatollah Ali Khamenei, a sign of his importance in Iran’s theocracy.

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In recent years, U.S. sanctions lists named him as heading Iran’s Organization for Defensive Innovation and Research. The State Department described that organization last year as working on “dual-use research and development activities, of which aspects are potentially useful for nuclear weapons and nuclear weapons delivery systems.”

Iran’s mission to the U.N., meanwhile, described Fakhrizadeh’s recent work as “development of the first indigenous COVID-19 test kit” and overseeing Tehran’s efforts at making a possible coronavirus vaccine.