Majid Jamali Fashi, 24, was convicted of killing Professor Massoud Ali Mohammadi by detonating a bomb outside his home in January 2010.

Fashi was also accused of being a spy for the Israeli intelligence agency Mossad and receiving $120,000 (£72,000) for the killing.

Israel does not comment on such claims.

"Majid Jamali Fashi, the Mossad spy and the person who assassinated Masoud Ali Mohammadi, our nation's nuclear scientist was hanged on Tuesday morning," Iran's Irna news agency reported.

Professor Massoud Ali Mohammadi was a particle physics professor at Tehran University. He is one of several high-profile nuclear scientists to have been killed in Tehran in recent years.

Iran has repeatedly accused Israel and the US of trying to harm its nuclear programme.

The two countries believe Iran is trying to acquire the technology to build nuclear weapons - something Tehran denies.

The country says it is developing its uranium enrichment program for peaceful purposes.

Fashi, who was tried and convicted in August 2011, appeared on Iranian TV in January confessing to the professor's killing, and giving details of the intelligence gathering operation he said he was involved in.

Opposition sources in Iran have accused the government of killing Professor Mohammadi because he was one of their supporters.