The 21 April bombing of the headquarters of Saudi Arabia's domestic security forces in the capital, Riyadh, marked the second significant tactical shift in recent months in the Islamic extremists' campaign to destabilise the kingdom.

The attack, carried out by Al-Qaeda, on such a high-value and well-guarded target in the centre of the capital, a symbol of the security apparatus that protects the royal family, was a message to the House of Saud that it is now in a fight for its very survival.

Assassination attempts against high-ranking Saudis are almost unheard of, although King Faisal was murdered by a disgruntled relative in 1975. But at least two high-ranking security officials have narrowly escaped attempts on their life in the last six months. Events that the government sought to hide from the public.

At the top of the terrorists' hit-list is the interior minister, Prince Nayef, and the defence minister, Prince Sultan. Both are reviled by reformers as arch-conservatives and are aligned with the puritanical and influential Wahhabi religious establishment. Sultan is seen as a traitor by some Islamic radicals for being too close to the US high command, while Nayef has become the nemesis of the militants inspired by Osama bin Laden, who want to bring down the pro-Western monarchy.

Until now, Westerners have borne the brunt of the militants' campaign. These attacks will continue, although possibly with even greater savagery than in the past. The militants have in recent days indicated that they want to copy the Yemeni and Iranian insurgents fighting in neighbouring Iraq who have kidnapped foreigners, mutilating and killing several Western captives. That would add a dangerous new dimension to the extremists' operations in Saudi Arabia.