As assassinations go, last Wednesday’s killing of an Iranian nuclear scientist was unusually competent. Mostafa Ahmadi Roshan, who worked at Iran’s Natanz Fuel Enrichment Plant, was blown up when a passing motorcyclist slapped a magnetic bomb onto his car that killed everyone inside but left the area around the vehicle unscathed. It was the fourth killing of an Iranian nuclear scientist in the last two years. An explosion at a missile base near Tehran on 12 November 2011 killed 18 people including Brigadier General Hassan Moghaddam, the architect of Iran’s missile programme. Take into account the Stuxnet computer virus that attacked the centrifuge system at Natanz, not to mention several defections of key scientific personnel, and it is clear that ‘non-diplomatic’ solutions to the Iranian impasse have become the norm.

The latest killing followed confirmation last week that Iran has begun enriching uranium at its underground plant at Fordo, prompting more international fears of an Iranian dash for a nuclear bomb. November’s blast followed an IAEA report that Iran had tested the fitting of a nuclear warhead onto its Shahab-3 missile. At the end of last year, Western powers vowed to sanction Iranian oil and a short while later an Iranian mob broke into the British embassy in Tehran. In response to Wednesday’s assassination, a government newspaper intimated that Iran’s Revolutionary Guards Corps might retaliate in kind. Iran has threatened to close the Straits of Hormuz through which 20 per cent of the world’s traded oil passes; if it does, Washington says it will reopen them by any mean necessary.

‘Tit for tat’ now seems inadequate to describe the dangerous escalation of arguably the world’s gravest political crisis. No one has claimed responsibility for the assassinations, explosions or cyber war, but Mossad is thought to be behind them and has done little to dispel the rumours. A couple of years ago I asked Dan Halutz, the former IDF chief of staff,whether Israel had indeed bombed a Syrian nuclear reactor in 2007. He smiled and said nothing. On Tuesday, Lieutenant-General Benny Gantz, Israel’s military chief of staff, informed a special parliamentary committee that Iran should expect more ‘unnatural’ events in 2012. Happy New Year.

It is hard to see what Israel gains from the assassinations. Trying to disable Iran’s nuclear programme one scientist at a time will take longer than solving the peace process. The argument that assassinations scare other scientists into resigning doesn’t seem plausible. Apart from anything else, Iran does not employ workplace guidelines that allow for the resignations of key personnel on projects of national importance. In fact, the tangible effect of the assassinations has already been seen: Iran hunkers down and speeds things up.

Much of this is to with political messaging. The Iranian message – ‘We are strong, you won’t push us about’ – meets its Israeli counterpart: ‘We are strong, we will push you about.’ A clash of obstinacies that in many ways echoes the last ten years of circulatory negotiations. It is also about frustration and a perceived lack of options. Diplomacy has gone nowhere; all-out war with Iran is, thankfully, unthinkable. I have never met a European, American or Israeli diplomat or politician who thinks it is a good idea (or who believes their country could afford it). It would be Iraq cubed.

As Norman Dombey has pointed out, an Iranian dash for the bomb would require the expulsion of IAEA inspectors, which the Americans are sure won’t happen. ‘If Iran did this,’ a White House staffer told me last year, ‘we would just bomb Natanz and they know it; they wouldn’t be so stupid.’ As far as military strikes against the Iranian reactors go, the logistical difficulties – with key facilities underground and spread out across a vast country – are severe. There is no appetite in the Pentagon for strikes, and while the Israelis leave the option ‘on the table’, their capability is less certain. ‘The Israelis tell us they can do it,’ the staffer told me, ‘our military says they can’t.’

So a covert, low-level campaign of attacks and killings it is then. But waging this sort of war is not without risks, including the risk of the undesirable escalation we are now seeing. As ever, much of the problem with Iran’s nuclear programme is Western fear of the programme. The Americans know that if they can’t show progress in slowing down enrichment or in getting Iran to turn over its stockpile of low-enriched uranium, pressure within the US and from Israel will rise. Israel might not be able to destroy all the programme’s facilities but it can do something. Washington is sure of its own red line, but for Israel, who knows?