Iran's parliamentary speaker has accused Israel and the United States of assassinating a scientist with possible links to the country's nuclear programme.

© UnknownDaryoosh Rezainejad was killed in Tehran
Darioush Rezainejad's death at the hands of motorcycle-riding gunmen prompted speculation that a violent and covert campaign to slow Iran's development of nuclear materials was again underway.

The 35-year old scientist was shot dead outside a kindergarten in east Tehran where he had gone to pick up his daughter. Mr Rezainejad's wife was wounded in the attack before the motorcyclists sped away.

The method of execution bore similarities to a spate of killings and attempted killings of Iranian nuclear scientists last year that involved assassins on motorcycles.

Ali Larijani, the hawkish speaker of the Iranian parliament, was quick to apportion blame.

"The American-Zionist terrorist attack yesterday against one of the country's scientists is yet another sign of the Americans' degree of animosity," he told MPs.

"American must think carefully about the consequences of such actions."

It is unclear what role, if any, Mr Rezainejad might have played in Iran's nuclear programme. Regime officials and the state media initially identified as a physics professor involved in the project, but later backtracked.

He was subsequently described as an electronics specialist working at the Iranian defence ministry or a master's student at a leading Tehran university.

State media sought to explain the discrepancy by saying that the dead man carried a similar name to a scientist who is involved in the project.

The killing comes amid growing western concern that Iran is rapidly accelerating its development of nuclear material and that it is now closer than ever to being able to produce a bomb.

International atomic inspectors say there is mounting evidence to suggest that Iran is preparing to install advanced "second-generation" centrifuges at an underground nuclear plant near the city of Qom. The regime kept the plant secret for many years but was forced to disclose its identity in 2009 after it was discovered by US intelligence.

Iran has also announced its intention to increase its production of uranium enriched to a level of 20 per cent purity, ostensibly so it can produce medical isotopes for a research reactor.

Iran would only need a further two or three months to convert the uranium into weapons-grade fissile material, according to senior western officials, including William Hague, the Foreign Secretary.

An apparent programme of sabotage and assassination is thought to have slowed Iran's nuclear production in recent years.

Last November, Majid Shahriari, a nuclear physicist, was killed after a passing motorcyclist waved his way through rush hour traffic and attached a sophisticated magnetic bomb to his car.

A few minutes later, Fereydoun Abbasi, who now heads Iran's Atomic Energy Association, narrowly avoided the same fate as he leapt clear of his car before a second magnetic bomb detonated.

A number of other senior officials linked to the nuclear project have either disappeared or died in mysterious circumstances since 2007.

In keeping with its policy of silence on intelligence matters, Israel has declined to comment on whether it was involved in any of these incidents, although a number of security experts have suggested that they bore the hallmarks of operations carried out by the Israeli intelligence agency Mossad.

For all the assassinations, however, it was the suspected deployment of a "cyber weapon" that seemed to prove most effective in slowing Iran's nuclear progress.

Mahmoud Ahmadinejad, the Iranian president, admitted late last year that the Stuxnet computer worm had damaged a number of the centrifuges used to enrich uranium at the country's nuclear reactors.

Dr Abbasi has now managed to solve the problems raised by Stuxnet and that the nuclear programme was now back on track.