Iranian nuclear scientist Dariush Rezaei was shot dead on Saturday when unknown assailants riding a motorcycle targeted him in the capital Tehran, local media reported.
"A physics professor and nuclear scientist was assassinated a few hours ago in front of his house in Tehran," Mehr news agency reported at 1430 GMT.
The ISNA news agency identified the scientist as Dariush Rezaei, 35, an expert with links to the Atomic Energy Organisation of Iran (AEOI).
Mehr said his wife was also wounded in the shooting and rushed to hospital.
According to the agency, Rezaei studied nuclear engineering in Tehran's Amir Kabir University and did research for the AEOI.
Several Iranian nuclear scientists have been murdered in recent years in attacks the Islamic republic has blamed on the United States and Israel, which suspect Iran's atomic programme masks a drive for a weapons capability.
Last November 29, Majid Shahriari was killed in the capital when men on motorcycles attached a bomb to his car, while the current nuclear chief Fereydoon Abbasi Davani survived a similar assassination attempt on the same day.
Abbasi Davani had been targeted by UN Security Council sanctions under Resolution 1747 adopted in March 2007. He was identified as a senior defence ministry and armed forces logistics scientist.
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The PhD holder in nuclear physics is one of the few Iranian specialists who can separate isotopes and has been a member of the elite military force the Revolutionary Guards since the 1979 Islamic revolution, media reports say.
Another senior Iranian nuclear scientist, Masoud Ali Mohammadi, was killed in a bomb attack on January 12, 2010, which Tehran blamed on "mercenaries" in the pay of the US and Israeli intelligence services.
Following the attacks, Tehran vowed to take measures to increase security for its nuclear scientists.
Iran is at loggerheads with the West over its nuclear programme, and the last round of talks between Tehran and the world powers broke down in Istanbul in January.
Iran is currently under four sets of UN Security Council sanctions over its refusal to suspend uranium enrichment. Several countries, including the United States and the European Union, have also imposed other unilateral punitive measures against Tehran.
Iran, however, remains adamant that it will push ahead with its controversial enrichment activities, which can produce either fuel for a nuclear reactor or the fissile material for an atomic warhead.
Tehran insists it will use the enriched uranium to fuel its future nuclear power plants, and that its atomic programme is entirely peaceful.
Nuclear chief Abbasi Davani, targeted by UN Security Council sanctions under Resolution 1747 adopted in March 2007, announced in June that Iran plans to triple its capacity to enrich uranium to 20 percent purity.