Iran on Sunday accused arch-foes the United States and Israel of masterminding the assassination of a scientist in Tehran, Dariush Rezaei-Nejad, who was reportedly associated with the defence ministry.
"The American-Zionist terrorist act yesterday against one of the country's scientists is yet another sign of the Americans' degree of animosity," speaker Ali Larijani told parliament on Sunday.
"America must think carefully about the consequences of such actions," he said, urging Iran's security forces to give a "stronger response to such evil moves."
Assailants riding a motorcycle shot dead Rezaei-Nejad, 35, in the capital on Saturday evening, according to the Iranian media which originally reported he was a nuclear scientist working for the Atomic Energy Organisation of Iran.
But on Sunday, the media stopped referring to him as a nuclear expert without giving an explanation, and presented him as an "electronics master's student" at Tehran's Khajeh Nassir University.
The Fars news agency suggested that the media had made a mistake in reporting Rezaei-Nejad's speciality, and insisted that he had links with the defence ministry, without giving details.
But higher education deputy minister Mohammad Mehdinejad Nouri told the Mehr news agency that the victim "was not a member of the defence ministry" and suggested that he may have collaborated on a project the ministry contracted to Khajeh Nassir University.
According to reports on Sunday, Rezaei-Nejad was shot five times by unknown assailants as he and his wife were waiting for their child in front of a kindergarten in Tehran. His wife was injured in the attack.
Tehran governor Morteza Tamaddon said at Rezaei-Nejad's funeral that the assassination "was without a doubt part of a project to discourage the Iranian nation from the path of (progress) it was pursuing," Mehr reported.
Tamaddon linked the murder to those who last year killed two top physicists working on Iran's controversial nuclear programme, Masoud Ali Mohammadi and Majid Shahriari.
"Nuclear energy is our undeniable right," chanted the crowd attending the funeral, according to Fars.
A statement signed by 200 lawmakers condemned what they called "the cowardly actions of America and the Zionist regime against the Islamic republic," particularly the "murder of an Iranian scientist."
Several Iranian nuclear scientists have disappeared in recent years or been targeted in attacks the Islamic republic has blamed on the United States and Israel, which suspect Tehran's atomic programme masks a nuclear weapons drive.
Tehran denies the charges, insisting that its atomic programme is entirely peaceful.
Iran is currently under four sets of UN Security Council sanctions over its refusal to suspend uranium enrichment. The US and the 27-member European Union have also imposed other unilateral punitive measures against Tehran.
The Islamic republic, however, remains adamant that it will push ahead with its controversial enrichment activities, which can produce either fuel for a nuclear reactor or the fissile material for an atomic warhead.
"In the field of scientific jihad, the blood of martyrs will allow Iran to continue its path", Tamaddon said on Sunday.
In Israel, there was no formal reaction to the allegation but an official said such charges were "routine."
"Iran routinely accuses Israel of all sorts of things," he told AFP on condition of anonymity.