The death of Mostafa Ahmadi Roshan was similar to killings of other Iranian nuclear scientists the Iranian government blamed on Israel and the United States -- and both countries denied -- The Daily Telegraph reported Wednesday.
Obama administration deputy press secretary Josh Earnest told reporters any suggestion the United States, which is at odds with Iran over its nuclear aspirations, was somehow involved in the attack is "categorically not true."
"The United States condemns this kind of violence," he said. "... This is exactly the kind of violence that we unequivocally condemn."
A person who was in the car with Roshan when the bomb detonated died later of injuries he sustained in the explosion, the Tehran Times said.
Officials said a motorcycle rider attached a magnetic bomb to the vehicle carrying Roshan and the other person.
The Web site of Sharif University in Tehran, where Roshan, 32, a chemistry expert, graduated, said the scientist "has been working as the deputy in charge of commerce at the Natanz site."
"The responsibility of this explosion falls on the Zionist regime," Tehran province Gov. Safar Ali Bratloo told Iran's Arabic-language al-Alam broadcaster. "The method of this terrorist action is similar to previous actions that targeted Iran's nuclear scientists."
There was no immediate response from Israeli officials, the Telegraph said.
The blast occurred outside the campus of Allameh Tabatai University, where the report said Roshan was a lecturer, reports from Iran indicated.
Western nations charge Iran is trying to develop nuclear weapons capability and have stepped up sanctions to try to halt its progress. Iran maintains its nuclear program is for peaceful purposes.