A powerful bomb blast killed one of Iran's leading nuclear scientists this morning in a leafy north Tehran district as he left home for work, officials said.
Massoud Ali-Mohammadi, 50, was described by colleagues as a respected Tehran University nuclear physicist. Reformist websites and two students also described him as an outspoken supporter of opposition figure Mir-Hossein Mousavi.
But hard-line Iranian officials immediately blamed Israel and the West for the assassination, which came at a time of heightened tension over Iran's nuclear program.
State television described Ali-Mohammadi as a "revolutionary university professor martyred in a terrorist operation by counterrevolutionary agents affiliated" with the West.
"Considering the kind of attack and previous threats by security and terrorist services close to America and the Zionist regime, probably this terrorist attack was sponsored by those services," said a report on the news website, Tabnak.
The West and Israel have vowed to prevent Iran from obtaining nuclear weapons capability. Iran's top diplomat last month accused the United States and Saudi Arabia of kidnapping nuclear scientist Shahram Amiri, who worked for Iran's Atomic Energy Organization, during a summer religious pilgrimage to Saudi Arabia.
But Iran is also in the grips of its greatest domestic crisis since the 1979 revolution, with political violence escalating. Even Iran's Supreme Leader Ali Khamenei demanded that pro-government vigilantes rein in their activities following the assassination of Mousavi's nephew in December and an alleged attack on opposition figure Mehdi Karroubi last week.
Though hard-line news outlets described Ali-Mohammadi as a former member of the Revolutionary Guard, a stalwart supporter of the Islamic Republic and a loyalist to Khamenei, others contradicted that assessment.
Dr Ali Moqari, president of the science department at Tehran University, told the Mehr news agency that Ali-Mohammadi "had no political activity."
One student of nuclear physics told The Times she believed Ali-Mohammadi was killed because of his outspoken support for the student movement. Another said Ali-Mohammadi cut his ties with the Revolutionary Guard years ago and in recent months had vocally turned against the Islamic Republic.
"Since two months ago, he has been venting his frustration with almost everybody in the system," said the student, who spoke on condition of anonymity. "He was openly criticizing high-ranking officials in classes."
The reformist news websites Ayandenews and Rahesabz identified Ali-Mohammadi among a list of scholars campaigning for Mousavi during his presidential run against President Mahmoud Ahmadinejad.
A graduate of Tehran's Sharif University of Technology, Ali-Mohammadi began teaching quantum physics and electromagnetic theory at Tehran University in 1995. He has written books on nuclear science and advised PhD candidates on their dissertations.
Officials offered different explanations for the source of the bomb. Some said it was attached to a motorcycle. Another said it was in a trash bin and set to detonate by remote control.
Neighbors said Ali-Mohammadi has lived for decades in an old bungalow set amid new multi-story apartment buildings on a quiet side street off north Tehran's Shariati Street.
Iranian news reports say he was leaving home for work when the explosion erupted. Witnesses said the 7:30 a.m. explosion shattered windows for 150 to 300 feet around.
"Most probably, the bomb had been fixed to the motorcycle outside Mr. Ali-Mohammadi's house, and exploded by remote control," Fakhreddin Ja'arzadeh, a Tehran prosecutor, told the Iranian Students News Agency.
Two people were reported injured and a car was set ablaze, witnesses and news reports said.
"I was shocked," said one resident, who spoke on condition of anonymity. "I was at breakfast, and our glass breakfast table shattered."
Police cordoned off the area as utility workers tried to restore downed power lines.
Iranian officials said forensic experts were conducting post-mortem examinations, but that no suspects had been arrested.
Mostaghim is a special correspondent.