By Aisha Labi

A University of Tehran professor who was killed in a bomb blast outside his home in the Iranian capital this morning was an outspoken supporter of the opposition politician Mir Hossein Moussavi who had encouraged students in their recent antigovernment protests, a student at the university said in an e-mail message from Tehran.

The student's characterization of Massoud Ali Mohammadi, a physics professor at Iran's leading higher-education institution, was at odds with the depiction of him in the state-controlled Iranian news media. Press TV, one such outlet, initially described Mr. Mohammadi as a nuclear physicist and "a staunch supporter of the Islamic Revolution" whose "assassination" had been carried out by agents of the United States and Israel, whose agenda it said included the kidnapping and killing of Iranian scientists.

Press TV quoted a University of Tehran colleague of Mr. Mohammadi as saying that the university's professors "widely" believed his killing had been orchestrated by the West.

But in a succession of e-mail messages, the student, who is active in the opposition movement and who spoke on the condition of anonymity out of fear of retribution, insisted that Mr. Mohammadi was not the ardent supporter of the regime that government news outlets have claimed.

"He was famous among his students for his bravery in defending them," the student wrote, saying that several hundred students gathered in commemoration today as word of his killing spread.

Mr. Mohammadi was an active supporter of Mr. Moussavi, whose defeat in the disputed presidential election in June served as the catalyst for sometimes-violent protests that have erupted in recent months in cities and on campuses across Iran. Mr. Mohammadi, the student said, was closely affiliated with the opposition movement, which has adopted the color green as its symbol.

"He was green," the student wrote. "He encouraged us to continue our resistance and our fighting for freedom."

The student speculated that the bombing, in which a remote-controlled explosive attached to a bicycle blew up, was a political assassination by Iranian security forces, part of a "dirty war" in which the regime has taken aim at its political enemies but blamed the attacks on the opposition or the West.

Another student who studied with Mr. Mohammadi described the slain professor as one of the few who was prepared to stand up to the university's administration and defend his students against attack. In the early phase of the protest movement, soon after the disputed election, dormitories at the university were brutally raided by security forces.