Saudi King Fahd (search) vowed to capture those responsible for a weekend bombing that killed 17 people at a compound housing mostly Arab foreigners in the Saudi capital.
In a Cabinet meeting held on Monday, Fahd said the kingdom "will strike with an iron fist all those who try to meddle with the security of the country and the stability and safety of its citizens and residentsm," the Saudi Press Agency reported.
The U.S. Embassy slightly eased restrictions on its staff and families Monday after the bombing in Riyadh (search).
Security was tight elsewhere in Saudi Arabia, though, amid fears of more attacks like Saturday's homicide car blast that also wounded scores of people. Officials have said the bombing bore similarities to previous Al Qaeda (search)-suspected operations.
On Tuesday, an Arab weekly that has received purported Al Qaeda statements in the past said Al Qaeda had claimed responsibility for the Riyadh bombing. It was the first claim of responsibility for the bombing.
"We struck Muhaya compound," the London-based weekly Al-Majalla quoted an e-mail from a purported Al Qaeda operative identified as Abu Mohammed al-Ablaj as saying, referring to the residential compound attacked Saturday.
The magazine, which appears on Fridays, said the e-mail was first seen late Monday and released a statement about it to The Associated Press on Tuesday.
Also on Tuesday, Reuters news service reported that Saudi security forces had detained a group fo suspects believed to be involved in Saturday's deadly bombing.
U.S. Deputy Secretary of State Richard Armitage, during a tour of the Middle East over the past few days and in comments Monday on Al-Arabiya television, said the attack appeared aimed at bringing down Saudi Arabia's ruling royal family.
After a review of the threat level, U.S. Embassy staff and their families were told they could travel outside Riyadh's heavily guarded diplomatic quarter, to which they had been restricted since the attack, an embassy spokeswoman said.
The embassy, which had closed Saturday before the bombing because of warnings of an imminent terror attack, is shut indefinitely. The State Department has made no decision to evacuate diplomats or dependents.
Also Monday, the U.S. Embassy in Sudan announced it will be closed until Sunday "as a result of a credible and specific threat to U.S. interests in Khartoum." The statement did not elaborate on the threat and urged U.S. citizens in Sudan to exercise caution.
Saudi authorities, who have clashed recently with suspected Al Qaeda militants, said earlier this month they were increasing security in the holy city of Mecca. Security officials were particularly concerned about the last 10 days of the fasting month of Ramadan, when some 2 million Muslims are expected to perform the "omra," or minor pilgrimage, to Mecca. Ramadan ends around Nov. 24.
After a Nov. 3 shootout in Mecca that left two suspects dead, Saudi authorities confiscated a large cache of weapons in the city, birthplace of the Muslim Prophet Muhammad, leading to fears a strike was planned in Mecca.
Saturday's car bombing was portrayed by Saudis as proof of the Al Qaeda network's willingness to shed Arab and Muslim blood as well in its zeal to bring down the U.S.-linked Saudi monarchy.
Al Qaeda, led by Saudi-born multimillionaire Usama bin Laden, has long opposed the royal family, accusing it of being insufficiently Islamic and too close to the West, particularly the United States.
At least 13 of those killed were Arabs, with four still unidentified, an Interior Ministry official told the official Saudi news agency. Five were children. In addition, 122 people were injured, most of them Arabs.
U.S. intelligence officials were uncertain Monday whether Al Qaeda deliberately targeted the compound of primarily Arab Lebanese. They suggested Al Qaeda may have made a miscalculation in killing Arabs, saying pictures of wounded women and children appearing on televisions throughout the Islamic could hurt Al Qaeda's cause.
One official, speaking on the condition of anonymity, said U.S. intelligence received enough information beforehand to warn that the attack was coming but not enough to pinpoint its location or identify the people who carried it out.
The United States joined countries around the world in expressing condolences and pledging to stand by Saudi Arabia in the war on terror. Armitage, who was in Egypt on Monday after visiting Saudi Arabia the previous day, said the attack was more evidence the war on terror was far from over.
"Our president, after the events of Sept. 11, said he was preparing our nation for a long war, and the more we looked at the phenomenon of Al Qaeda, the more we became convinced there is going to be a long struggle," Armitage said.
The Sept. 11 attacks on the United States also were blamed on Al Qaeda.
In Riyadh, Armitage pledged Americans "will be fully participating partners, if that is the desire of the kingdom of Saudi Arabia" in its anti-terror fight.
The Saudi ambassador to Britain, Prince Turki al-Faisal, cited similarities between Saturday's bombings and previous Al Qaeda strikes. Saudi officials blame Al Qaeda for a series of car bombings May 12 on three Riyadh compounds housing foreigners. Those attacks killed 35 people, including nine homicide bombers.
The Associated Press contributed to this report.