Iran's president has blamed Israel for the killing of a top nuclear scientist on Friday, and said it would not slow down the country's nuclear programme.
Hassan Rouhani also said Iran would retaliate over Mohsen Fakhrizadeh's killing at a time of its choosing.
Fakhrizadeh was killed in an ambush on his car by gunmen in the town of Absard, east of the capital Tehran.
Israel has not commented, but it has previously accused him of being behind a covert nuclear weapons programme.
Fakhrizadeh was Iran's most renowned nuclear scientist, who headed the ministry of defence's research and innovation organisation.
His killing threatens to escalate tensions over Iran's nuclear programme with the US and its close ally Israel.
How has Iran reacted?
President Rouhani said his country would respond "in due course" but that Fakhrizadeh's killing would not push Iran into making hasty decisions, in televised comments 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 a televised cabinet meeting.
"In due time, they will answer for this crime," he added.
In an earlier statement, the president accused the "the mercenaries of the oppressive Zionist regime" - referring to Israel - of being behind the attack.
"The assassination of martyr Fakhrizadeh shows our enemies' despair and the depth of their hatred... His martyrdom will not slow down our achievements."
There has been no comment from Israel on the killing. The New York Times quotes three US officials, including two intelligence officials, as saying Israel was behind the attack.
Fakhrizadeh's name was specifically mentioned in Israeli PM Benjamin Netanyahu's presentation about Iran's nuclear programme in April 2018.
Hossein Dehghan, military adviser to Supreme Leader Ayatollah Ali Khamenei, vowed to "strike" the perpetrators like thunder.
Foreign Minister Mohammad Javad Zarif called on the international community to "condemn this act of state terror".
Source: BBC