The method of the assassination was all too familiar. The motorcycle with the pillion passenger, the magnetic bomb and the lifeless body left in the car. This is the fifth attack on an Iranian nuclear scientist. In four cases, including Wednesday's assassination of Mostafa Ahmadi Roshan, the results have been fatal.

What is different this time is the level of tension that surrounds the murder. Naval war games have been performed in the Gulf and more are planned. There is a war of words between Iran and Washington over the flow of oil through the Strait of Hormuz, the choke point in the Gulf that Iran threatens to close.

The level of stress in the west's confrontation with Tehran is about to be raised yet again with a new EU oil embargo, due to take effect in six months' time, according to an agreement in principle in Brussels.

There are some get-out clauses, with a review in three and six months to assess the impact on the oil price, but the news is likely to draw more defiance from the government in Tehran.

The European embargo is due to coincide with US measures targeting the financing of the Iranian oil trade, effective in June – an attempt forced through by a combative Congress in December to strangle the Iranian economy. Even some US commentators think this could be equivalent to a declaration of war.

"The Obama administration has no intention of going to war with Iran," said Trita Parsi, author of a new book on Obama's policy on Iran, entitled A Single Roll of the Dice. "But the administration wants to create a credible threat of war, in the belief that Iran only responds to such credible threats.

"However, there is little confidence they can contain that threat. The vote on the sanctions in the Senate showed that their control of Congress is very limited."

In the midst of this volatile situation, the killing of another Iranian nuclear scientist has all the potential of a struck match at an explosives dump.

Parsi said the Israelis, well aware they cannot destroy the Iranian programme on their own, have a motive for lighting the match.

Whether it is responsible or not, the Israeli military establishment has a motive to claim successes in the covert war on Iran, as General Benny Gantz did this week, because it is under political pressure to start an overt one. The generals, however, know that Israeli air strikes would unleash a war without accomplishing their goal of destroying the Iranian nuclear programme.

A covert war, based on assassinations and sabotage, may appear a better alternative. Individual killings may not seriously hinder a large, wide-ranging programme, but they would certainly deter young Iranians from taking that line of work.

However, such a campaign is not without huge risks for the region. Elements of the Iranian establishment seem to be lashing out in frustration. Last October's bomb plot against the Saudi ambassador and Israeli diplomats in Washington, alleged to be the work of the Iranian Revolutionary Guard, was amateurish and reckless.

Likewise, the storming of the British embassy, on the anniversary of Majid Shahriari's assassination, appeared to have gone much further than the leadership intended, and deepened Tehran's isolation.

"The old guys at the top are losing control of the situation," a senior western diplomat observed, the day before this latest killing.

The fragmentation of the regime will have unpredictable, and possibly very violent, outcomes. Whoever is killing Iran's scientists is clearly willing to risk catastrophic consequences that could engulf the region.