Radical Islamist attacks on Muslims are opening a chasm between themselves and more moderate Muslims who have been sympathetic, or at least indifferent, up until now.

The tactic will not only backfire on al-Qa'eda, say security officials, but will help the intelligence services gain support in a conservative society where tribal taboos prevents people from informing on other clan members.

In slaughtering women and children, the terrorists broke the code that binds tribal Muslims, handing police a unique opportunity to infiltrate the dozens of terrorist cells in Saudi Arabia, where al-Qa'eda gains much financial and ideological support.

Information from tribal leaders and the public on terrorist activities soared following last May's attacks on western compounds in Riyadh, enabling police to smash a huge number of cells and arrest more than 600 suspects in the past six months.

As it shut down terrorist operations and tightened the net around terrorist activities in the kingdom, Saudi security gained enough intelligence to warn, almost to the day, that al-Qa'eda was planning a big attack.

The choice for Saturday's attack was considered a relatively "soft"target in comparison to compounds housing westerners where security has been raised to the point where they are believed vulnerable only to rockets and missiles.

Intelligence officials believe that as Saudi security forces closed in on home-grown terrorist cells, they caused a degree of panic. The terrorists feared that their weapons and explosives dumps might be discovered and "it became a case of use it or lose it," one western security official said yesterday.