Iran on Sunday sentenced to death a man accused of playing a key role in the 2010 murder of a top nuclear scientist and of spying for Israel, the official IRNA news agency reported.

"The sentence to execute the terrorist Majid Jamali Fashi ... has been issued" for the assassination of scientist Masoud Ali Mohammadi, Iran's prosecutor general Gholam Hossein Mohseni Ejeie said, quoted by IRNA.

Mohseni Ejeie, who is also spokesman for the Iranian judiciary, said the sentence was passed on Sunday, less than a week after the opening of Jamali Fashi's trial.

His defence lawyers have 20 days to launch an appeal.

Jamali Fashi stood trial as the main suspect in the killing of Ali Mohammadi, a particle physics professor at Tehran University who was killed in a bomb attack outside his home in January 2010.

He was accused of "Moharebe (waging war against God) using assassination as the means ... by placing a bomb-laden bike in front of Ali Mohammadi's house," the state television website reported.

It quoted the prosecutor in the trial which opened on August 23 and lasted a single session.

Jamali Fashi also faced charges of cooperating with Israel's spy agency and of having received $120,000 for passing on intelligence to Mossad, the website report added.

The Islamic republic has blamed the Jewish state and the United States for the unexplained disappearances of several of its military officials and nuclear scientists.

Western powers and Israel suspect Iran is seeking an atomic weapons capability under the guise of its civilian nuclear and space programmes, a charge Tehran vehemently denies.