Saudi king vows to strike with 'iron fist'
U.S. ready to help kingdom fight terrorism if asked
Workers sift the rubble at the site of the bombing Monday.
CNN's David Ensor reports on the possibility that the latest terror attack could backfire on al Qaeda.
CNN's Mimi Mees reports that analysts say the Saudi government is now targeted by an Islamist movement it once supported.
Saudi security officials say they expect another terrorist attack.
The U.S. is sending a mixed message to Saudi Arabia. CNN's Chris Plante reports
RIYADH, Saudi Arabia (CNN) -- Saudi Arabia's King Fahd pledged Monday that he would strike militants with an "iron fist" in the wake of a weekend car bombing in Riyadh that killed at least 17 people, government sources said.
During a meeting with his Cabinet, Fahd also said he wants to make sure it is safe for people to travel to Mecca during the Muslim holy month of Ramadan, the sources said.
Mecca, the birthplace of the prophet Muhammad, is Islam's holiest city, and hundreds of thousands of pilgrims travel there during Ramadan.
Fahd's vow to crack down on the militants came as officials warned that more attacks could come at any time.
Saudi officials tightened security at diplomatic compounds and other sensitive sites, and sent 4,600 troops to Mecca, sources said. (Full story)
Saudi officials blamed Saturday's suicide car bombing in a mostly Arab neighborhood in Riyadh on al Qaeda. (Full story)
Among the dead were five children, and 122 people were wounded, the Saudi Press Agency said.
Sources in the Saudi government told CNN Monday that al Qaeda might have targeted the complex mistakenly believing it housed Americans.
The sources said Saudi authorities learned that information while interrogating an al Qaeda suspect already in their custody.
Saudi sources said one car blew up in the attack, and that they suspect a second vehicle was used, although that is still under investigation. Witnesses reported hearing multiple explosions.
U.S. officials said Monday that intelligence suggested al Qaeda was planning more attacks in Saudi Arabia.
"This is not the end," a senior State Department official said. "There are still people at large who want to hurt us, and we think there may be more."
The official said such attacks "could be in the operational phase."
The attack came a day after the United States ordered its embassy and consulates in the kingdom temporarily closed because of concerns that terrorists may be planning to launch an attack.
On Monday, two senior U.S. State Department officials said the U.S. Embassy in Khartoum, Sudan, would be closed through the week because of an unspecified threat. (Full story)
U.S. Deputy Secretary of State Richard Armitage pledged "continued U.S. cooperation with the Saudi government against terrorism" when he met Sunday with Crown Prince Abdullah, said State Department spokesman Richard Boucher in Washington.
"The deputy secretary said we will be fully participating partners if that is the desire of the kingdom of Saudi Arabia," Boucher said.
Arriving Monday in Cairo, Egypt, Armitage commended Saudi efforts after near-simultaneous car bombings in May at Riyadh housing complexes that killed 23 people, in addition to the 12 bombers.
But he added: "We, the defenders, have to be right 100 percent of the time, and the terrorists only have to be right once."
Boucher said U.S. and Saudi authorities have been working together to round up terrorists, but Saturday's attack underscored the need to do more.
As for who was behind the attack, Boucher said, "It looks like al Qaeda. It smells like al Qaeda. It has all the earmarks of al Qaeda."
One U.S. official said the attack could backfire on al Qaeda by turning more Arabs against the group.
The official noted that in the period since the May attacks in Riyadh, many of the U.S. troops who were based in Saudi Arabia have left the kingdom.
"That makes it all the more clear that their goal is to overthrow the Saudi monarchy," he said.
A spokesman for the Saudi Embassy in Washington told CNN that the government believed that might be the terrorists' motive.
"What we are looking at is a group of people that are committed to overthrow the Saudi state, to create an Afghan-type Taliban rule in Saudi Arabia," Nail al-Jubeir said. "We're not going to have them succeed."
Boucher said the attack made it clear that "al Qaeda, presumably, or whoever is responsible for this attack, is not just going after Westerners or foreigners. They're going after Arabs as well.
"They're going after everybody, including the Saudi government -- everybody who is trying to organize society and move in a positive direction."
The Saudi Press Agency said those wounded included Jordanians, Palestinians, Indians, Pakistanis, Sudanese, Ethiopians, Eritreans, Indonesians, Filipinos, Turks, Sri Lankans and Romanians.
A delegation from the Lebanese Foreign Ministry arrived in Riyadh to help that nation's citizens cope with the attack, the Lebanese consul said.
Consul Ali Ghazawi said three Lebanese from the same family -- a father, mother and son -- were missing. He said four Lebanese died in the attack, though the Saudi Press Agency said seven.
The car that exploded Saturday night left a crater in the center of the neighborhood, which was littered with rubble and burned-out vehicles. Witnesses initially reported hearing multiple explosions.
CNN's Nic Robertson, David Ensor, Nada el-Housseini, Elise Labott and Sandy Petrykowski contributed to this report.