"Charges of US involvement are absurd," State Department spokesman Mark Toner said, after Iran's foreign ministry accused US and Israeli "mercenaries" of being behind the bomb plot.
Massoud Ali Mohammadi, a particle physics professor at prestigious Tehran University, died when a bomb strapped to a parked motorcycle was triggered by remote control outside his home in northern Tehran, state media said.
Tehran's foreign ministry spokesman Ramin Mehmanparast was quoted in Iranian media as seeing "signs of evilness by the triangle of the Zionist regime, America and their mercenaries in Iran in this terrorist incident."
He vowed that Iran would not be deterred from its nuclear efforts, however.
"Such terrorist acts and the physical elimination of the country's nuclear scientists will certainly not stop the scientific and technological process but will speed it up," he said.
Iran's chief prosecutor also implicated US and Israeli intelligence services in the bombing that killed nuclear scientist Massoud Ali Mohammadi.
"Given the fact that Massoud Ali Mohammadi was a nuclear scientist, the CIA and Mossad services and agents most likely have had a hand in it," Abbas Jafari Dolatabadi told state media Tuesday.
