Iran's president has said the country would retaliate over the killing of Mohsen Fakhrizadeh, the country's most senior nuclear scientist who was assassinated on Friday outside Tehran.
Hassan Rouhani also said Iran would take action "in due course" but the incident would not push the country into making hasty decisions, in a televised statement on Saturday.
"Iran's enemies should know that the people of Iran and officials are braver than to leave this criminal act unanswered," he said.
"In due time, they will answer for this crime," he added.
Fakhrizadeh was killed while driving through the city of Absard, east of Tehran, by “armed terrorist elements” using explosives and machine-gun fire, the Iranian state broadcaster said.
He died at a local hospital where medical staff were unable to revive him.
Photographs released by the Iranian news agency Fars showed a Nissan sedan with bullet holes through its windshield and pools of blood on the road.
The country’s Foreign Minister Mohammad Javad Zarif said there were “serious indications of [an] Israeli role”.
He added in a tweet: “Iran calls on int'l community—and especially EU—to end their shameful double standards & condemn this act of state terror.”
Rouhani said in a previous statement that "the mercenaries of the oppressive Zionist regime", apparently referring to Israel, were responsible for the killing.
Hossein Salami, the chief commanded of Iran’s elite Revolutionary Guard, said: “Assassinating nuclear scientists is the most violent confrontation to prevent us from reaching modern science.”
There was no immediate comment from Israel, although Prime Minister Benjamin Netanyahu has referred to Fakhrizadeh at a previous news conference saying: “Remember that name.”
Both US and Israeli intelligence have described him as a driving force behind the Iranian nuclear weapons programme that the International Atomic Energy Agency (IAEA) said was ended in 2003.
But the agencies alleged Fakhrizadeh continued to work on the project even after it was formally disbanded.
IAEA inspectors now monitor Iranian nuclear sites as part of Iran's now-unravelling nuclear deal with world powers.