Iran's supreme leader demanded on Saturday the "definitive punishment" of those who masterminded the killing of the country's top scientist who spearheaded a disbanded military nuclear program.

Iranian President Hassan Rouhani blamed Israel for the killing. The West has long suspected the scientist of reviving Iran's secret nuclear weapons program.

On Saturday night, the family of Mohsen Fakhrizadeh gathered at a mosque for his funeral service in central Tehran, an Iranian state broadcast reported.

Israel, long accused of killing Iranian scientists 10 years ago in the wake of frictions over the Islamic republic's nuclear ambitions, has yet to comment on the death of Mohsen Fakhrizadeh, who was killed in an explosion and a hail of bullets near Tehran, Friday.

The assassination had revived fears of Iran retaliating on the U.S., Israel's closest ally in the region, as the country did earlier this year when a U.S. drone strike killed Iran's top military general, Qassem Soleimani.

Iranian officials have since said the true revenge for Soleimani's killing will be the full withdrawal of American troops from Iraq. The Iranian authorities have vowed to exact "harsh revenge."

In Tehran, a small group of hardline demonstrators set on fire images of Trump and President-elect Joe Biden, who has said that his incoming administration will consider revisiting a nuclear agreement with Tehran with world powers.

Tehran's nuclear program has continued its experiments and currently enriches uranium up to 4.5 percent -- far below weapons-grade standard levels of 90 percent. Military experts believe Tehran has enough low-enriched uranium to build at least two nuclear bombs.

Both Saudi Arabia and Israel are worried about the changing atmosphere of politics in the Middle East and its outcome once Biden takes office.

"The killing of martyr Fakhrizadeh shows our enemies' despair and the magnitude of their hatred. His martyrdom won't slow down our achievements," Rouhani disclosed in a statement, according to state television.

According to analysts, when Rouhani refers to Iran's "enemies," he is evidently talking about the Trump administration, Israel, and Saudi Arabia.

The killing comes just days before the 10th anniversary of the assassination of top Iranian nuclear scientist Majid Shahriari that Iran also blamed on Israel.

On Saturday, the Pentagon said it had deployed the USS Nimitz aircraft carrier back to the Middle East hours after the killing. As a symbol of American military power, the carrier might also prove a deterrent to any hostile acts by Iran.