Iran received information days ago that Israeli and US intelligence intended to carry out "terrorist acts" in Tehran, its parliament speaker said on Wednesday, after the killing of a university scientist.
Iranian officials and state media described the slain man as a nuclear scientist, but a spokesman said he did not work for the Atomic Energy Organization at the centre of Iran's disputed nuclear program.
Iran's influential parliament speaker, Ali Larijani, said a US-based pro-monarchy group had claimed responsibility for the attack, adding the group was controlled by the CIA. Iran's Fars News Agency on Tuesday said such an exile group had claimed the bombing in a statement, without saying how it obtained it.
"An American-based monarchy group ... claimed responsibility for this terrorist act," Larijani said, the state broadcaster reported. "Maybe the CIA and the Zionist regime (Israel) thought they can mislead us with such an absurd statement."
"We had clear information several days ago that the intelligence apparatus of the Zionist regime and the CIA wanted to implement terrorist acts in Tehran," he said.
Using such a "rootless group" as a cover was a new "disgrace" for US President Barack Obama, Larijani said. "Why do you host this terrorist group in America?" he asked.
The head of a pro-government Islamic militia, Basij, called for "revenge" for the bomb attack.
"We should take revenge for these crimes (committed) by America and, God willing, it will happen," Mohammad-reza Naqdi was quoted as saying by ISNA news agency.
In Washington on Tuesday, a US intelligence official said the CIA had played no role in the incident in Tehran.
Tuesday's bombing – a rare attack in the Iranian capital – occurred at a time of heightened tension in the Islamic Republic, seven months after a disputed presidential election plunged the major oil producer into turmoil.
It also coincided with a sensitive time in Iran's row with the West over its nuclear ambitions, with major powers expected to meet in New York on Saturday to discuss possible new sanctions on Tehran over its refusal to halt its atomic work.
A list of Ali-Mohammadi's publications on Tehran University's website suggested his specialism was theoretical particle physics, not nuclear energy, a Western physics professor said on Tuesday.
The West suspects Iran's nuclear work is aimed at developing bombs. Tehran says it seeks only to generate electricity.
State media described Ali-Mohammadi as a "committed and revolutionary" professor, suggesting he backed the government of hardline President Mahmoud Ahmadinejad.
But an opposition website, Jaras, said he was an opposition supporter who backed moderate candidate Mirhossein Mousavi in last June's disputed election, which plunged Iran into turmoil.
Iran has been convulsed by its most serious domestic unrest since the Islamic revolution in 1979, as protests by opposition supporters against the election result have turned violent. Authorities deny opposition allegations that voting was rigged.