An Iranian nuclear scientist was assassinated yesterday in Tehran by a magnetic bomb fixed to his car in an attack the authorities have blamed on Israel and which will deepen the confrontation over Iran's nuclear programme.
Iran says the death of Mostafa Ahmadi Roshan, a chemistry expert and a director of the Natanz uranium enrichment facility, is part of a covert war being waged by the Israeli, British and US intelligence services inside Iran.
Witnesses said two people on a motorcycle had stuck the bomb to the scientist's Peugeot 405 near Gol Nabi Street in north Tehran. It exploded, killing the scientist, injuring another person in the car who later died in hospital, and wounding an 85-year-old passer-by.
"The bomb was the same as the ones previously used for the assassination of scientists, and is the work of the Zionists," Tehran's deputy governor Safarali Baratlou told the semi-official Fars news agency. Officials said the latest killing would not affect the nuclear programme.
A similar bomb blew up in a specially rigged motorcycle on 12 January 2010 – killing a Tehran quantum physics professor, Massoud Ali Mohammadi. Later that year one of Iran's most important nuclear scientists, Majid Shahriyari, an expert on nuclear chain reactions, was assassinated while he was driving to work. He and his wife were targeted with another magnetic bomb placed on the driver's door by a motorcyclist on 29 November.
The fact the killers knew the movements of their victims so precisely suggests the involvement of foreign intelligence services using Iranians belonging to dissident movements. Israel has refused to comment officially but on Tuesday, its chief of staff, Lt-Gen Benny Gantz, reportedly told a parliamentary panel that 2012 would be a "critical year" for Iran in part because of "things that happen to it unnaturally".
One mystery is why Mr Roshan was unprotected by bodyguards and was so easy to attack if he was important to Iran's nuclear programme. Iran said this week that it was expanding a facility to make enriched uranium south of Tehran in a bunker protected by 300ft of rock. This makes it surprising the authorities should have allowed crucial scientists to drive around Tehran in civilian cars without any protection.
Iran has a tradition of seeking revenge for any attack since the overthrow of the Shah in 1979 started decades of confrontation with the US in which planes have been shot down, ships sunk, officials and militants kidnapped, and partisans of both sides killed. So far, it has not retaliated for the assassinations of the scientists, though its inability to keep them safe will be seen as a sign of weakness.
While the identity of those carrying out the assassinations remains a mystery, it is most likely to be Israel's foreign intelligence service, Mossad, reportedly working with the Mojahedin-e-Khalq, a cult-like long-time opponent of the Islamic government in Tehran. It was for many years allied to Saddam Hussein and based in Iraq, but is thought to still have agents in Iran.
The tit-for-tat attacks and threats exchanged between Washington and Tehran have reached an intensity not seen since 1988, when the US Navy came close to joining the Iran-Iraq war on Iraq's side. The belief that angry rhetoric and a low-level covert war being waged against Iran by its foreign enemies might escalate into a real military conflict has driven up oil prices to $113 a barrel for Brent crude since the start of the year.
The US is heavily involved in this undercover war against Iran. At the beginning of 2008, President Bush won secret approval from Congress to spend $400m to launch a campaign to destabilise the clerical leadership in Tehran. As well as gathering information on a possible nuclear weapons programme, it was aimed at supporting dissident minorities inside Iran such as Baluchis, Kurds and Arabs in the south-west of the country.
Clandestine operations were carried out inside Iran that included seizing members of al-Quds, a commando arm of the Iranian Revolutionary Guard. Baluchi groups based in Pakistan claimed responsibility for bomb attacks in south-east Iran against Revolutionary Guard targets.
The US has also been accused of supporting Pejak, a Kurdish group based in Iraqi Kurdistan which is connected to the Turkish Kurd PKK and carries out raids across the border into Iran. Although Pejak officials claim contacts with the US, the group is small and has limited influence. Some of its former leaders allege that it is infiltrated by Iranian intelligence.
Despite the escalating crisis over Iran's nuclear programme, the US has found no evidence Tehran is trying to make a nuclear bomb, though US politicians often speak as if this was an established fact. The US Defence Secretary, Leon Panetta, went out of his way last weekend to deny that Iran was trying to build a nuclear device. He said that if it did so this would be a "red line" for the US.
The US National Intelligence Estimates on Iranian nuclear progress, the collective judgement of all the US intelligence organisations, said there was no evidence Iran had been trying to build a bomb since 2003. The Defence Intelligence Agency concluded that Iran's nuclear weapons programme at that time was directed against Saddam Hussein's Iraq and when he was overthrown by the US, it was ended.
A secret nuclear war? Previous victims
Ahmadi Roshan Director of Natanz uranium enrichment facility killed by magnetic car bomb.
Darioush Rezaeinejad Shot dead by men on motorbikes in Tehran last year. He was initially described as a scientist working on Iran's nuclear programme but this was later denied. Analysts blamed the CIA and Mossad for his death.
Majid Shahriyari Killed by a car bomb attached in Tehran. The academic was "in charge of one of the great projects" at a nuclear facility according to Ali Akbar Salehi, the head of the nuclear programme.
Fereidoun Abbasi (survived) The attack on Mr Shahriyari was co-ordinated with another on Mr Abbasi, which left the latter wounded. He was appointed head of Iran's atomic agency soon afterwards.
Massoud Ali Mohammadi The particle physicist and opposition politician was killed when a motorcycle strapped with explosives was remotely detonated near his car.
Ardeshir Hosseinpour (unconfirmed) The scientist's death from gas poisoning was reported by Iranian TV a week after it happened, sparking rumours that Mossad might be to blame.