Tehran, Iran (CNN) -- The Iranian Foreign Ministry said the nuclear scientist killed in a bombing Tuesday was assassinated and the act "revealed signs of the involvement of the Zionist regime, the U.S. and their allies in Iran," state media reported.
Strongly condemning the killing of Massoud Ali-Mohammadi, ministry spokesman Ramin Mehman-Parast said the participation of Israeli and American agents "runs counter to international regulations," Press TV reported.
However, a senior U.S. administration official said charges that the United States was behind the killing is "absurd." Israel has not commented.
Mehman-Parast said such actions would not affect Iran's nuclear program, emphasizing such "terrorist moves and apparent omission of Iranian nuclear scientists will definitely cause no obstacle in the way of the country's scientific and technological development. Rather they will speed up it."
Superintendent of Tehran's Criminal Court Fakhreddin Jafarzade told Fars News Agency that initial investigations indicate the attack was carried out at 7:58 a.m. local time, that the bomb had been planted on a motorcycle outside Ali-Mohammadi's home in Tehran's northern neighborhood of Qeytariyeh, and that it caused instant death.
"Investigations show that the bomb was triggered by a close-range remote control device," Jafarzade said.
Not long after the killing, Iranian media were reporting a claim of responsibility from the Royal Association of Iran, which Press TV characterized as an "obscure monarchist group that seeks to reestablish the Pahlavi reign in Iran," a reference to the Shah of Iran's regime which was toppled in the 1979 Islamic Revolution.
During the revolution, Ayatollah Khomeini returned from exile to become Iran's supreme leader and the country was renamed the Islamic Republic of Iran.
Press TV said the Royal Association of Iran is headed by Foroud Fouladvand, and is responsible for a deadly bombing in the southern city of Shiraz in April 2008 that killed 13 people and wounded hundreds more.
Fars reported that "members of this association had infiltrated into the country and had been active in the post-election riots of last June and played a part in setting public property on fire and inciting people to riot.
"It had been established during trials (of some of the members of this association) it had been established that they were in charge of showing people how to make Molotov cocktails and setting public places on fire."
It is unclear where the academic stood politically.
Tehran's Prosecutor Abbas Jafari-Dolatabadi said Ali-Mohammadi taught neutron nuclear physics at Tehran University, Press TV reported, and the network said Ali-Mohammadi was a staunch supporter of the Islamic Revolution.
Head of the Science Complex of the University of Tehran Ali Moqari told Mehr News Agency Tuesday that Ali-Mohammadi "was a prominent international figure, but had not been involved in any political activities." He said the professor was prominent in his field and had written books.
Ali-Mohammadi's name has appeared on an opposition site on a list of academics backing the Iranian opposition.
And, according to Fars, the Royal Association's statement said Ali-Mohammadi played "an active role during the recent disturbances in Tehran, dresses as a plainclothesman," a common reference to police and others working with security forces to quell riots.
"We declare with pride that we are Mohareb (those who wage war against God), yes, we are Mohareb," the association said, according to Fars.
Tehran University professor Mohammad Marandi, quoted by Press TV, reported that Ali-Mohammadi's colleagues believe "he was assassinated by terrorist organizations probably supported by the United States and has connections with the Americans and the Israelis under different names."
There has been talk among Marandi's colleagues and a news report that a group called the People's Mujahedeen Organization of Iran was behind the attack. But that group, an Iranian dissident group based in Iraq, has denied the allegation.
Grass-roots outrage has swept Iran over the disputed presidential elections in June, when incumbent Mahmoud Ahmadinejad won a second term. Hundreds of thousands of Iranians took to the streets to demonstrate against the official result, and that prompted a forceful and sometimes deadly government crackdown.