Iran's clerical and military rulers have threatened revenge for Friday's killing of Mohsen Fakhrizadeh, which could further increase tensions in the Middle East region and beyond.
"Our people are wiser than to fall in the trap of the Zionist regime (Israel) ... Iran will surely respond to the martyrdom of our scientist at the proper time," Rouhani said in a televised cabinet meeting.
"Once again, the evil hands of Global Arrogance and the Zionist (Israeli) mercenaries were stained with the blood of an Iranian son," Rouhani said in a statement earlier on Saturday, adding that Fakhrizadeh's death will not slow down Iran's nuclear work.
Israel has declined to comment on the killing.
The death of Fakhrizadeh could provoke confrontation between Iran and its foes in the last weeks of Donald Trump's U.S. presidency. It could also complicate any effort by President-elect Joe Biden to revive the detente of Barack Obama's presidency once he takes office in January.
The White House, Pentagon, U.S. State Department and CIA have declined to comment, as has Biden's transition team.
At least four scientists were killed between 2010 and 2012 in what Tehran said was a program of assassinations aimed at sabotaging its nuclear energy program. Iran has always denied pursuing nuclear weapons.
The semi-official Tasnim news agency reported that after an explosive-laden car exploded near Fakhrizadeh's vehicle around 2:30 pm local time, one of the assassins began to spray bullets at his car.
It said one of Fakhrizadeh's bodyguards was shot four times and Fakhrizadeh was transported by helicopter to a hospital in Absard town at Damavand county some 70 km (44 miles) east of Tehran. He died in the hospital.
One witness told state TV that there were repeated gunshots and Fakhrizadeh's bodyguards clashed with the assassins.
