By Martin Asser
BBC News Online
Another bloody attack in Saudi Arabia means another massive blow to international confidence in the oil-rich Gulf kingdom.
Many questions are raised by the incident in Khobar, in which 22 civilians were killed - about the security of foreign workers, the state's ability to combat extremist Islamist violence, and even about the future stability of the global economy.
Most worryingly, the frequency of militant attacks in Saudi Arabia appears to be increasing.
On 12 May 2003 the kingdom received its wake-up call - a co-ordinated suicide bombing of three housing compounds for foreigners in the capital Riyadh that left 35 people, including nine bombers, dead.
The attack on Oasis compound in Khobar is the latest in a series
At the time it was described as the kingdom's own 9/11 - galvanising the Saudi authorities in the eyes of the Bush administration into taking its first serious steps to join the US "global war on terrorism".
But although the Saudis have rounded up more than 600 suspects and killed a number of men on a wanted list that contained at one point 29 names, attacks by al-Qaeda supporters have continued, and - in some respects - gained sophistication.
On 8 November, 17 people died when another compound, this time one for Arab families, was hit - right on the doorstep of one of the royal palaces in Riyadh.
And the most sustained period of attacks started on 21 April 2004, when a Riyadh police headquarters was struck by a suicide attacker, killing four people.
Then came a gun rampage at a petrochemical company on 1 May in the Red Sea port of Yanbu which left six Westerners and a Saudi dead.
Three of the gunmen apparently worked at the company and used their entry passes to gain access to their victims - one of whom was paraded through the streets in a grisly ritual that seems to have been repeated in the latest atrocity.
Only a week ago, a German citizen was gunned down by unidentified attackers on a Riyadh street.
There are two schools of thought regarding Saudi Arabia's security problem.
Saudi officials insist this is the last gasp of a movement that the state has done everything to shut down, through strong policing, good intelligence, and curbing the very ideology that produces these attacks.
Officials say six terrorist cells were identified in the last year, consisting of about 25-to-30 members each. They say five of the six have now been smashed by the security forces.
The string of attacks has perplexed Saudi Arabia
However, Saudi ambassador to the UK Prince Turki al-Faisal - himself a former Saudi intelligence chief - has told the BBC that it will still be very difficult to scotch the movement entirely.
"These people are willing to kill themselves to achieve their purposes, it's practically impossible to prevent them totally from taking their action," he said.
Anger and hatred
The other school of thought holds that Saudi Arabia is incapable of quelling to the massive groundswell of anger and hatred towards the West engendered by the US-led invasion of Iraq and the Israel-Palestinian conflict that triggers such attacks.
Author and former CIA operative Robert Baer, for example, says the killings of the foreign workers in Khobar - in the Saudi oil producing heartland - are meant to send a message to the Opec meeting of oil exporting countries in Beirut later this week.
Accusations of complicity have dogged the security services
He says the militants are giving expression to many ordinary Saudis' discontent about government plans to increase production to bring world oil prices down, in particular to help the US economy.
And he doesn't rule out much more damaging attacks in the future.
"This most recent attack did not affect the supply of oil, but all Saudi Arabia's oil facilities are vulnerable and a determined effort could take one of these facilities out," Mr Baer says.
And even if the attacks are restricted to "pin-point" attacks like in Khobar, it is deterring investment and making foreign expertise harder and more expansive to bring into the kingdom - so the country is already suffering economically, even if no oil installation is hit.
Perhaps the darkest aspect of the latest incident is the suspicion of collusion between the attackers and the security forces.
Anti-terrorism experts told BBC News Online that they were surprised at the ease with which three of the four attackers were able to escape from the Oasis compound in Khobar, despite the overwhelming numerical superiority of the security forces and the tactical and logistical advantages which they enjoyed.
If true, the existence of collusion between attackers and the people meant to catch them would be most disturbing.
Prince Turki dismisses such a theory, arguing that the killers go for the softest targets and if they really did have helpers in positions of authority they would be able to attack much more high-profile targets causing "terrible destruction" .
Having said that, as any militant knows, you only have to kill one person to terrorise a thousand. To penetrate a compound in Khobar as they have done is enough to make every single foreign worker consider his or her position in the kingdom.