More terror attacks on Americans could be ahead, the State Dept. (search) has announced, warning U.S. citizens in Saudi Arabia to take extra precautions.

Late Thursday, U.S. officials warned Americans of possible attacks in Saudi Arabia's busy Red Sea port of Jiddah (search).

"(We have) received an unconfirmed report that a possible terrorist attack in the Al Hamra district of Jeddah may occur in the near future," the warning said. "U.S. citizens are encouraged to maintain a high level of vigilance."

An American official, who spoke on condition of anonymity, said intelligence "indicated that there was going to be a stream of attacks, and so we have confidence that has begun."

Attacks on three residential compounds in Riyadh (search) have thrown Saudi Arabia into turmoil, forcing its leaders to acknowledge that they may have been too complacent about terrorism.

Saudi soldiers and armed guards set up new checkpoints, searched cars and quizzed drivers by the hundreds as security was tightened throughout the jittery capital of Riyadh. Bumper-to-bumper traffic caused by the security checks stretched for miles.

The increased vigilance came after U.S. criticism that the Saudis had not done enough to prevent Monday's Al Qaeda-linked suicide bombings that killed 34 people, including eight Americans.

U.S. Ambassador Robert Jordan said was a "very clear suggestion that this attack was aimed at undermining the government as much as it was aimed at American interests."

Two of the compounds housed employees of the Saudi National Guard, headed by Crown Prince Abdullah, and air force workers in the Defense Ministry, which is led by Prince Sultan. Both are brothers of King Fahd.

The third complex is owned by the deputy governor of Riyadh, second only to the governor, Prince Salman, also a brother of the king.

In the Philippines, police said Friday they were looking for a Filipino worker who claimed in a radio interview that he was offered money in Saudi Arabia to bomb one of the residential compounds targeted this week.

The man, who refused to be identified, told Manila radio station DZMM on Friday that he befriended Arab-looking men who offered him a large sum of money in exchange for planting a bomb there. He said he returned to the Philippines in April for fear of his life.

Saudi officials say the attacks are linked to Usama bin Laden's Al Qaeda terror network, which has long vowed to rid Saudi Arabia, home to Islam's holiest sites, of any Western influence.

"This organization has always had the Saudi government in their sights," said Alex Standish, the editor of Jane's Intelligence Digest in London. "By targeting specifically foreigners working within the kingdom, it's ... economic sabotage."

Saudi Arabia is home to 6 million expatriate workers, including about 35,000 Americans and 30,000 Britons.

Standish said the American response -- advising U.S. citizens to leave -- is doing "exactly what Al Qaeda wants, which is an exodus of foreign labor."

Saudi officials have faced past criticism for doing too little to combat militancy ahead of the Sept. 11, 2001, attacks, which also were blamed on Al Qaeda. Fifteen of the 19 Sept. 11 hijackers came from Saudi Arabia.

Saudi columnist Sulaiman al-Hattan wrote Thursday in The New York Times that Saudi society had been exposed to "only one school of thought, one that teaches hatred of Jews, Christians and certain Muslims like Shiites and liberal and moderate Sunnis."

"We Saudis must acknowledge that our real enemy is religious fanaticism," he said urging for a start to reforms, especially in education.

Jordan, the U.S. ambassador, says beginning April 29 he sent three letters to the Saudi Interior Ministry requesting enhanced security at residential compounds. His May 7 letter came a day after a raid on a terrorist safe house near Jadawal, one of the three compounds attacked Monday.

The Washington Post reported that the view from the second floor of the safe house allowed the presumed attackers to case the Jadawal compound.

Some U.S experts are concerned the Saudis will limit American access to suspects and evidence, as they did after the 1996 bombing of the Khobar Towers, which killed 19 U.S. personnel.

But Jordan said he expects good cooperation from the Saudis. An FBI team arrived in the kingdom Thursday to determine what help is needed in the investigation.

Jordan believes that the Saudi-born bin Laden and Al Qaeda may have lost some support in the kingdom because of Monday's attacks.

"I think in some ways they have hurt themselves here," Jordan said. "They have gone too far and they have soiled the nest."

Other experts on terror disagreed.

"The fact that bin Laden has survived so long despite the fact that the world's last superpower is hunting him ... is building up quite a harmful myth among Al Qaeda supporters that this organization is under some kind of divine protection," said Standish.

"He is almost (seen as) the new Saladdin who is fighting this reverse crusade against the West."

The Associated Press contributed to this report.