Photo provided by the agency Fars car Majid Shahriari killed in an attack in Tehran.
File: Dr. Majid Shahriari before his assassination.
Assassins on motorbikes killed a top Iranian nuclear scientist and injured a second in James Bond-style hits.
They attached magnetised bombs to their cars which exploded within seconds as they drove to work in Tehran.
Iranian president Mahmoud Ahmadinejad immediately blamed Israel and other Western governments for the attacks.
Iranâ€™s nuclear chief Ali Akbar Salehi said the man killed, Majid Shahriari, was involved in a major project with the countryâ€™s nuclear agency.
Mr Shahriariâ€™s wife, who was in the car with him, was wounded.
The injured scientist, Fereidoun Abbasi, is believed to be a laser expert at Iranâ€™s Defence Ministry and one of the countryâ€™s few top specialists in nuclear isotope separation. His wife was also injured.
Iranian officials said they suspected the attacks were part of a covert campaign aimed at damaging the countryâ€™s nuclear programme.
America, Britain and other allies are determined to stop Tehran developing nuclear weapons.
Mr Ahmadinejad told a press conference that â€œundoubtedly, the hand of the Zionist regime and Western governments is involved in the assassinationâ€.
He also added that â€œenemies of Iranâ€ had used computer code to make â€œlimitedâ€ problems for centrifuges involved in uranium enrichment at some of its nuclear sites.
Mr Salehi issued a stern warning to the West as he rushed to hospital to see the surviving scientist.
â€œDonâ€™t play with fire. The patience of the Iranian nation has limits. If it runs out of patience, bad consequences will await enemies,â€ he said.
Asked about the Iranian accusations, Israeli government spokesman Mark Regev said Israel did not comment on such matters.
Washington has strongly denied any link to previous attacks.
A pro-government website said Mr Abbasi held a Ph.D. in nuclear physics and has long been a member of the Revolutionary Guard, the countryâ€™s most powerful military force.
It said he was also a lecturer at Imam Hossein University, affiliated to the Guard. The United States accuses the Guard of having a role in Iranâ€™s nuclear programme.
Todayâ€™s attacks bore close similarities to another in January that killed Tehran University professor Masoud Ali Mohammadi, a senior physics professor. He was killed when a bomb-rigged motorcycle exploded near his car as he was about to leave for work.
In 2007, state TV reported that nuclear scientist, Ardeshir Hosseinpour, died from gas poisoning.
A one-week delay in the reporting of his death prompted speculation about the cause, including that Israelâ€™s Mossad spy agency was to blame.
The latest attacks came as Tehran was left increasingly isolated by the WikiLeaks revelations which show that several Arab leaders, including King Abdullah of Saudi Arabia, have been urging America to launch military action to stop Iran developing nuclear bombs.