(RFE/RL) -- Iran has accused the United States and Israel of involvement in a bomb attack that killed a Tehran nuclear physics professor.
State media said Masud Ali Mohammadi was killed by a booby-trapped motorbike as he left his home in the capital this morning.
The U.S. State Department has rejected as "absurd" the allegations of U.S. involvement.
Iranian state media described the victim as a "staunch supporter of the Islamic Revolution."
But Radio Farda has spoken to people in Tehran who say Mohammadi had backed opposition leader Mir Hossein Musavi, and the professor's name appeared on a blog of Musavi backers. Authorities have accused
Musavi supporters and other critics of the June presidential election of seditious activities aimed at casting off the country's clerically dominated system.
"Reports say Doctor Masud Ali Mohammadi was killed after a motorbike parked near his home exploded," the news anchor on the Iranian state's English-language broadcaster, Press TV, said.
The report described Mohammadi as a teacher of "neutron physics" at Tehran University.
State Department spokesman Gordon Duguid said he could think of no reason why Tehran would make such an accusation.
"I'm not going to guess on this instance or other instances where charges are hurled about willy-nilly," Duguid said. "The fact remains [that] we are working within prescribed diplomatic channels to engage the government of Iran on their behavior. Their nuclear program is of particular concern to us, as you know, and that is what we are working with the government on."
Press TV footage showed a building with shattered windows, said to be Mohammadi's home in northern Tehran's Qeytariyeh neighborhood, and the pavement outside smeared with blood.
ISNA news agency quoted Tehran provincial deputy police chief Safarali Baratlou as confirming that Mohammadi was the only person killed in the blast.
Baratlou said the explosion appeared to have been set off by remote control, and that Mohammadi was driving away from his home when the bomb struck. Scientist And 'Revolutionary'
In the same report, Tehran prosecutor Abbas Jafari Dolatabadi called Mohammadi a "lecturer in nuclear energy" and said that no suspects had been arrested.
Quoting unnamed sources, another Iranian news agency, Borna, called Mohammadi a "senior nuclear scientist of the country."
State broadcaster IRIB described Mohammadi as a "committed and revolutionary" professor killed by "antirevolutionary and arrogant powers' elements."
Iranian officials frequently refer to perceived Western foes as "the global arrogance."
Iranian state media also described Mohammadi as "a committed and revolutionary" professor, suggesting he supported the government of President Mahmud Ahmadinejad.
But RFE/RL's Radio Farda reports that Mohammadi's name appears on setadnet.mihanblog.com, a blog of supporters at Iranian universities of opposition leader and defeated presidential candidate Musavi.
The name is among 420 Tehran University lecturers who signed a letter, posted on the blog two days before the June presidential election, supporting Musavi's candidacy.
The disputed election result and the protests that followed plunged Iran into its most sever political turmoil in decades.
A Tehran journalist who wished to remain anonymous told Radio Farda that Mohammadi was not considered a prominent opposition member.
But another source claimed that the professor's opposition leanings were no secret.
"His [Mohammadi's] political position in supporting Musavi [was] not hidden to anybody," the man said. "He was one of Musavi's supporters and was well-known as a Green movement supporter."
The man said Mohammadi had given a speech to students less than a week before his death in which he outlined his prescription for getting out of the current crisis.
Mohammadi "showed his political position, that he was pro-Musavi and pro-Green movement, and he criticized the reaction of the government after the presidential election in that speech," he said. Questionable Claim
Iranian media quoted a statement by a pro-monarchist group, the Association of Iran's Monarchy, claiming responsibility for the blast.
A spokesman for the group later denied that report, saying the claim appeared on a fake website that bore his association's name. He speculated that authorities had set up the bogus site.
Mohammadi's killing comes with international tension high over Iran's disputed nuclear program.
A spokesman for Iran's atomic agency, Ali Shirzadian, told AP that Mohammadi was not connected to his agency.
An Iranian TV grab shows Mohammadi's body being taken away from the scene.
Notwithstanding Tehran's denials, the West suspects Iran's program is aimed at developing a nuclear weapons capability.
Another Iranian nuclear scientist, Shahram Amiri, disappeared in the middle of last year while on a pilgrimage to Saudi Arabia, raising questions about whether he defected and gave the West information on Iran's nuclear program.
In December, Tehran accused Saudi Arabia of handing Amiri over to the United States.
The killing also comes as Iran faces its worst domestic unrest since the Islamic revolution in 1979.
It was triggered by the disputed presidential election in June, which the opposition says was rigged in favor of Ahmadinejad -- a charge authorities deny.
At least eight people were killed in clashes between security forces and opposition supporters on Ashura, the day of ritual Shi'ite mourning on December 27.