JERUSALEM (Reuters) - If Mossad assassins were behind the killing of an Iranian nuclear scientist on Wednesday, it would be the latest chapter in a long history of Israeli covert action against foes best not confronted with full force.
As always, Israeli officials declined any comment on the death of Mostafa Ahmadi-Roshan, who was blown up in his car, while Iran itself immediately pinned the blame on Israel.
Cold-eyed calculus guides what Israeli officials call "precision thwarting", a euphemism that strives to focus blame on those marked for death while conveying reluctance to escalate the shadow war.
Critics condemn all such attacks on moral grounds, and also question the long-term efficiency of targeted killings, but Israeli officials, drawing on years of experience in the murky practice, believe they play a vital role in defending the state.
When it comes to Iran, whose uranium enrichment and ballistic missile projects have suffered a surge of spectacular and often bloody mishaps in recent months, Israel measures the gains in terms of the delays they cause.
"They are not keeping to the schedules they would like to keep to," former Mossad spymaster Meir Dagan said in a recent television interview, smilingly crediting the apparent sabotage spree to "God, who controls everything".
The daylight killings of atomic technicians such as Ahmadi-Roshan -- who, like others before him, fell victim to an explosive device attached to his car by a passing motorcyclist -- obviously deplete Iran's pool of nuclear experts.
It also provokes panic in surviving colleagues, said an Israel official, generating a phenomenon that Mossad veterans dub "virtual defection".
"It's not that we've been seeing mass resignations, but rather a sense of spreading paranoia given the degree to which their security has been compromised," the official, who has extensive Iran expertise, told Reuters.
"It means they have to take more precautions, including, perhaps, being a little less keen to stand out for excellence in their nuclear work. That slows things down."
HISTORY OF HITS
The activation this week of an Iranian enrichment plant deep in a mountain drew condemnation from world powers which, along with many Gulf Arabs, see bomb-making potential in a nuclear programme that Tehran insists is for peaceful energy needs.
Ahmadi-Roshan was at least the third expert linked to Iran's nuclear programme to be killed in the last two years.
"I don't know who settled the score with the Iranian scientist, but I am definitely not shedding any tears," Israel's army spokesman Yoav Mordechai said on his Facebook page.
Happy to deflect the blame, Israeli officials say many people have an interest in sabotaging Iranian operations.
"I think several players, not only Israel, are active (in Iran)," former Mossad deputy director Ilan Mizrahi said on Wednesday. "It's not only countries, it is movements. You have the Iranian opposition, which is very strong. They have their own capabilities inside Iran."
Yet Israel has an admitted history of state-sponsored assassination and intimidation, from letter-bombs it sent German scientists serving Egypt's missile programme in the 1960s to the Mossad hunt, using guns and booby-traps, for Palestinians involved in killing 11 Israeli athletes at the 1972 Olympics.
More recently, Israeli air-launched missiles and special forces picked off Palestinian uprising leaders. In 1995, motorbike-borne gunmen killed Islamic Jihad chief Fathi Shiqaqi in Malta, and another suspected Mossad team smothered Hamas commander Mahmoud al-Mabhouh in his Dubai hotel in 2010.
Proponents of such tactics say they stave off more ruinous open war and few voices are raised in Israel in condemnation. Mabhouh had helped smuggle rockets to Palestinians, a threat Israel cited in justifying its 2008-2009 offensive on the Gaza Strip, amid international outcry at the high civilian toll.
"When you are fighting terror, targeting the heads of terror organisations is positive," Mizrahi said, justifying killings.
Against Iran's nuclear programme, Israel - like the United States - has hinted it could resort to military force.
But neither is keen to further destabilise the region by opening a new Muslim front, and military experts say Israel alone does not have the firepower to kill off Iran's nuclear programme in a single swoop.
Assassinations carry their own incalculable risks, as the Mossad learned in 1997 when the men it sent to poison Hamas leader Khaled Meshaal in Amman bungled the job and were caught.
Israeli Prime Minister Benjamin Netanyahu, then in his first term, had ordered the hit under pressure to retaliate for Hamas suicide bombings. He ended up having to repair ties with Jordan by freeing Hamas's spiritual mentor, Sheikh Ahmed Yassin, from prison -- an unexpected boon for Palestinian radicals.
Despite widespread speculation, Iran denied Israeli sabotage was to blame for a blast last November that killed a Revolutionary Guards general. On Wednesday it was swift not only to blame Israel, but also to publish the sensitive nature of the victim's work at the uranium enrichment facility of Natanz.
"The Iranians are exposing this in order, ultimately, to provide a large degree of rationale and justification, both domestically and abroad, for what they will eventually consider as a reprisal," said Uzi Rabi, a Middle East expert at Tel Aviv University.
He predicted an "unavoidable showdown", most likely in the Gulf, where Iran has threatened to close the strategic Strait of Hormuz, with a possible spillover in the form of Israeli and Western air strikes on Iran.
(Additional reporting by Crispian Balmer; Editing by Tim Pearce)