By Roger Hardy BBC Middle East analyst

Saudi Arabia is reeling from the shock of a major suicide attack on a residential compound by suspected al-Qaeda militants in the capital Riyadh - the second in six months.

The suicide attack has claimed 11 lives so far

The compound housed mainly Arabs from outside Saudi Arabia and women and children are reported to among the casualties.

The suicide attack could mark an escalation of Osama Bin Laden's war against the ruling princes of Saudi Arabia.

The attack on the Al-Muhaya housing complex had the hallmarks of an al-Qaeda operation. Synchronised suicide attacks have become one of their specialities.

Whether the bombers knew that the complex housed mainly Arabs from outside Saudi Arabia is not clear.

It is possible they thought that among the residents were Americans working for Boeing, the US aerospace company, as had been the case in the past.

Targeting Saudi

It is equally possible they regard Arabs living alongside Westerners as fair game.

Bin Laden has not always targeted the land of his birth. His violent jihad, or holy war, was initially directed first and foremost at America.

Some analysts speculated that the Saudi princes had bought off al-Qaeda, to prevent attacks on their soil.

But everything changed when suspected al-Qaeda militants launched triple suicide bombings in Riyadh six months ago.

Those attacks, too, targeted compounds housing foreigners. The 35 dead were of several nationalities - Americans, Saudis, Filipinos and others.

Some Saudis refer to that day, 12 May, as their own 9/11.

The blasts caused widespread damage at the compound

Following those attacks, the gloves came off. The Saudi princes realised Bin Laden was now committed to the violent overthrow of a regime he regarded as illegitimate.

They launched an unprecedented crackdown on Islamic militants.

Suspected al-Qaeda cells were discovered in Riyadh, Mecca and other cities. Hundreds of suspects were arrested, some as young as 15 or 16.

Senior princes and top religious figures made speeches denouncing extremism and intolerance. Hundreds of imams (prayer leaders at mosques) were sacked or sent for retraining.

Yet, despite these efforts, it is evident that al-Qaeda has a well-rooted network of activists in the kingdom.

And the group and its leader enjoy a greater degree of support from some sections of the population than the authorities care to admit.

This latest attack shows how far they are from winning the war against the enemy within.