A car-bomb exploded this week in Saudi Arabia's capital despite heightened security alerts in the oil-rich kingdom. Though no one was injured in the attack, four car bombs earlier this year in Riyadh killed more than 50 people and injured more than 100 others.
Saudi officials call the deadly attacks, which began May 12 in Riyadh, a wake-up call.
"It was our September 11, May 12," said business executive Abdulmuhsin al Akkas, a member of Saudi Arabia's parliament, the Majlis ash Shura. "The real September 11 took us by surprise that many of us went into disbelief. We did not believe that 15 Saudis could do such a thing. We hear [people] here and there screaming their heads off about this or that, but to actually commit the crime, we could not believe it. And therefore we went into denial. But it took a while to realize they are Saudis and we have to deal with it."
He says the Riyadh bombings now have brought the problem home.
Saudi and U.S. officials say terrorists with links to al-Qaida are trying to destabilize the government. Al-Qaida leader Osama bin Laden, a Saudi national, has targeted Western interests in the oil-rich kingdom and the royal family that has ruled for more than 70 years.
Western diplomats says there is a reserve of ready recruits for al-Qaida among zealous Saudi religious fighters who returned home after ousting the Russians from Afghanistan two decades ago, as well as among disgruntled youngsters raised in an ultra-conservative Wahabi branch of Islam that portrays Westerners as infidels.
The U.S. Embassy has issued several alerts for non-essential diplomats and Americans to be more vigilant or consider leaving Saudi Arabia.
American businessman Jim Greenberg has lived and worked in Saudi Arabia for more than two decades. His family lives in an upscale Riyadh housing compound for Westerners with 370 homes, a restaurant, shops, and recreational facilities all nestled behind a three-meter-high stucco wall.
He says that tranquil life was shattered after the May bombings. "Immediately after May 12 we had the armored cars here, armored vehicles with machine guns and Saudi soldiers," he said. "And gradually from there we built up the additional security with greater standoff distance, concrete barricades. The barricades were also here during the  Gulf War, but not the Saudi soldiers, not the multiple checkpoints."
It is not only Westerners who are feeling jumpy. Medical student Amal Sowayan thinks twice about going downtown. "After the bombing, I think when I am in the car, the next one will blow up," he described. "I have this thought a lot, and I never had this before. I feel insecure, unsafe a lot."
In a massive crackdown since May, the government has arrested hundreds of suspects and confiscated hidden stockpiles of weapons.
Newspapers have published photos of the most-wanted terrorists and encouraged the public to provide tips to help catch them.
Saudi officials have curbed the flow of funds to overseas Islamic charities that U.S. officials suspect are financing terrorist networks. And patrols have been increased along the borders with Yemen and Iraq to stop arms smuggling.
Mohammed al Hulwah believes the terrorists have miscalculated by targeting Saudi Arabia, which is home to Islam's holiest shrines. Mr. Hulwah heads the Majlis ash Shura's foreign relations committee.
"For the terrorist group the big mistake that they start to fight and bomb in Saudi Arabia, because now the government reverses the direction," he said. "And now the holy war is to fight these terrorists because they threaten Saudi Arabia and [want to] destroy its reputation in the world and [work] against the interests of Islam."
Pro-reform Majlis member Abdulmuhsin al Akkas says the fight against terrorism also needs to deal with a sub-culture of xenophobia and intolerance.
"These are persons committing crimes on our streets," he said. "So the first order of business is for security agencies to stop them and take them into custody. This is not negotiable. Second thing is [that] apparently the most immediate thing is the intellectual atmosphere that encouraged extremism. So what is needed to bring new atmosphere where tolerance is the norm and not the exception."
Saudi Arabia's government is undertaking political and economic reforms. Educators are reviewing curriculum and textbooks that critics say offered a harsh, intolerant view of the world.
The government has removed hundreds of radical clerics.
But pro-reform Saudis say the campaign against terrorism and the pace of reform depend on how quickly Saudi Arabia's rulers can modernize a traditionally closed society without alienating the conservative religious establishment said to underpin their legitimacy.