Tehran, Iran CNN  — 

Iran’s Supreme Leader Ayatollah Seyyed Ali Khamenei has vowed revenge after the killing of the country’s chief nuclear scientist, as top officials pile blame on Israel.

Mohsen Fakhrizadeh, who became the face of Iran’s controversial nuclear program, was killed in a district east of Tehran on Friday, in what Iranian officials are calling an assassination.

“There are two matters that people in charge should put in their to do list: 1- To follow up the atrocity and retaliate against those who were responsible for it. 2- To follow up Martyr Fakhrizadeh’s scientific and technical activities in all fields in which he was active,” Khamenei wrote Saturday in a tweet from an account often attributed to him, making a veiled reference to the country’s nuclear activities.

He added: “Our distinguished nuclear scientist in the defense of our country, Mr Mohsen Fakhrizadeh was killed by the oppressive enemies. This rare scientific mind lost his life for his everlasting great scientific work. He lost his life for God and the supreme leader. God shall reward him greatly.”

ANALYSIS: Killing humiliates Iran. But no one in the world’s most febrile region wants war

Iranian Defense Minister Brig. Gen. Amir Hatami said Fakhrizadeh was ambushed by gunmen and targeted by a Nissan vehicle explosion before a firefight ensued, semi-official news agency ISNA reported.

A view of the scene where Mohsen Fakhrizadeh was killed, in Absard, Iran on Friday.

At a cabinet meeting Saturday, Iranian President Hassan Rouhani also said the country would retaliate and pointed to Israel for orchestrating the attack. “The think tanks and the enemies of Iran must know that the Iranian nation and the officials in charge in the country are brave and determined to respond to the murder in time,” he said.

He added that the killing was carried out at “the filthy hands of oppressors, in concert with the illegitimate Zionist regime.”

Iranian Foreign Minister Javad Zarif on Friday called the killing “cowardice – with serious indications of Israeli role.”

Iran has provided no evidence of Israeli involvement. Israeli Prime Minister Benjamin Netanyahu’s office declined to comment to CNN on Friday.

Speaking on Israel’s Channel 12 news Saturday evening, Israeli cabinet minister Tzachi Hanegbi said he had “no idea” who assassinated Fakhrizadeh – but called it “very embarrassing for Iran.”

In April 2018, Netanyahu mentioned Fakhrizadeh by name when he unveiled a nuclear archive that he said Israeli agents had smuggled out of Iran. He called him the head of a secret nuclear project called Project Amad. “Remember that name, Fakhrizadeh,” Netanyahu told reporters.

Fakhrizadeh is also mentioned in multiple reports by the US State Department and the International Atomic Energy Agency as holding deep insight into Iran’s nuclear capabilities.

Funeral arrangements

The funeral and burial of Fakhrizadeh will take place Monday, according to the semi-official Fars News Agency, which did not specify a location.

In an earlier report, Fars said the remains of Fakhrizadeh will be taken Saturday on a pilgrimage to the shrine of Imam Reza for blessing in the northeastern city of Mashhad. Afterward, his body will be taken back to Tehran for a final visit to the tomb of Ayatollah Khomeini, the founder of the Islamic republic.

Killing ‘a big deal,’ US official says

Fakhrizadeh was head of the research center of new technology in the elite Revolutionary Guards, and