Israeli diplomats and Iranian nuclear scientists now have something in common: the danger of being killed by a magnetic car bomb.

The technique has now been used against members of both groups. Israel denies involvement in such murders, the most recent one last month, of Iranian scientists. Iran denies responsibility for car-bombings this week against Israeli envoys in Tbilisi and Delhi. Men reportedly carrying Iranian identity papers were arrested after a botched magnet-bomb attack in Bangkok on Tuesday; Thai officials say Israeli diplomats were the intended targets.

In the furtive world of undercover violence, it is never easy for the world to be sure about who did what. Cases with genuine "smoking gun" evidence, such as Mossad's murder of Hamas commander Mahmoud Al Mabhouh in Dubai two years ago, are the exception, not the rule.

Certainly, Israel has no shortage of enemies. Nor does Iran, which also is undergoing a particularly opaque power struggle among religious authorities, elected politicians and the Republican Guard. Iran uses Hizbollah operatives for some of its dirty work; Israel is said to be in league with the Iranian exile group MEK.

Iran's secret services are considered to be sophisticated and capable, but those are not words which could be used about this week's bombers, nor about a murky alleged Iranian plot, exposed last year, to kill the Saudi ambassador to Washington. It is, in short, very difficult to be certain who is killing, or trying to kill, whom.

It is however not difficult to see that this cannot end well if it continues to escalate. Targeted killings can easily lead to retaliation against higher-placed targets.

Tensions are high and rising between Iran and Israel, with various parties and factions in both countries doing what they can to both pander to and manipulate public opinion. Will Israel try to bomb Iran's nuclear installations? Will Washington? Republican challengers to President Barack Obama are tripping over each other to show solidarity with Israel.

Despite the increasing pain of ever-tighter sanctions, meanwhile, Iran persists in its programme, announcing a new milestone just yesterday.

The stakes are too high for all this brinkmanship. Instead of playing with matches, leaders in both countries - in all countries - have a plain duty to lower Iran-Israel tensions. The threatening rhetoric only serves the purposes of the assassins planning the attacks.