Updated

Saudi officials did not respond to American requests for extra security at residential compounds in Riyadh (search) in the face of warnings of imminent Al Qaeda (search) terrorism, the U.S. ambassador said Wednesday.

Whether extra guards would have stopped the assaults Monday on the three compounds is unclear, but Ambassador Robert Jordan (search) suggested the Saudis had not done enough to fight terrorism.

"We contacted the Saudi government, in fact on several occasions, to request that added security be provided to all Western residential compounds and government installations in the kingdom," Jordan said on CBS' The Early Show. "But they did not, as of the time of this tragic event, provide the additional security we requested."

The Saudi ambassador to the United States, Prince Bandar bin Sultan, acknowledged the request in interviews on CBS and ABC, but suggested that Jordan requested security for only one compound -- and that Saudi security successfully protected foreigners at the site.

"He asked for increased security at a certain compound," Prince Bandar told CBS News. "We have passed it to the right authority, and that compound that he was concerned about was the only place that the evil people who did this attack did not cause injuries except killing the Saudi guards."

Prince Bandar was apparently referring to the attack on the Eshbiliya complex, where two Saudis were killed.

The Saudi foreign minister Prince Saud al-Faisal, said he had not heard of any such request but acknowledged the bombings showed problems within his country's security effort.

"The fact that the terrorism happened is an indication of shortcomings, and we have to learn from our mistakes and seek to improve our performance in this respect," he said at a news conference. "Each time the American Embassy or any other embassy seeks the intensification of security measures, the government fulfills this request."

Before Monday, Saud said, "there was news coming from everywhere that they were planning a major attack."

But U.S. and Saudi officials said the warnings provided no specifics of location or time.

Several U.S. officials said even if security had been improved at the compounds, it is unlikely the attacks could have been stopped, given the number of attackers armed with automatic weapons.

In Washington, a State Department official said American and Saudi officials would look at how the security issues were handled in the days preceding the explosion.

Saudi officials may have provided extra police patrols for a day or two, but then pulled them, one U.S. Embassy consular official said.

Suspicion that Al Qaeda carried out the attacks grew Wednesday as a six-member FBI team made its way to Riyadh to assist the investigation. After being delayed in Germany, the agents were expected to arrive in the kingdom on Thursday.

The team was kept small to prevent the perception that U.S. law enforcement officials were taking over, according to FBI officials. The group will determine what other personnel and resources need to be brought in.

Saudi cooperation with the U.S. investigators could be critical. Some U.S. experts worry the Saudis will limit American access to suspects and evidence, as they did after the 1996 bombing of the Khobar Towers military dormitory that left 19 American service members dead.

But current and former officials said the relationship between Saudi police and U.S. investigators has improved since the earlier bombing, which American counterterrorism officials say was carried out not by Al Qaeda but a group called Saudi Hezbollah.

"I think there has been a realization that the terrorist threat is real and could come home with a vengeance to the kingdom in Saudi Arabia as it has come home to us in the United States," said Rep. Porter Goss, R-Fla., chairman of the House Intelligence Committee.

After Monday's car bombings, the State Department ordered nonessential diplomats and family members out of Saudi Arabia. Other Americans in Riyadh moved to a U.S. military compound outside of town.

Saudi officials linked the attacks to an alleged Al Qaeda cell they had been hunting in recent weeks. They said 15 Saudis took part in the strikes, nine of whom appear to have perished as homicide bombers.

On May 7, the Saudis had raided a suspected safehouse for that cell and confiscated explosives and guns. Several suspects escaped.

U.S counterterrorism officials said it was possible the Saudis headed off an even larger attack with the raid, forcing Al Qaeda operatives to go forward with a less potent strike than they were planning.

The officials said the question of who directed the operation remains to be answered. They listed several possibilities: senior Al Qaeda operatives, including the son of Usama bin Laden, who are hiding in Iran, and top Al Qaeda operatives inside Saudi Arabia.

Among Al Qaeda's top men in the kingdom is one known as Abu Bakr al-Azdi, a key operational planner, U.S. officials said. His real name is Ali Abd al-Rahman al-Faqasi al-Ghamdi, the officials said.

U.S. officials had initially said that Abu Bakr, using another name, sent e-mails to a London magazine last weekend that appeared to announce the impending attack. Officials now say the signer, Abu Mohammed al-Ablaj, is another Al Qaeda operative, but his e-mails are still regarded as credible evidence of Al Qaeda's involvement.

Another operative involved in Saudi operations is Khalid al-Juhani, who appeared with other suspected Al Qaeda operatives on a "martyrdom video" that U.S. forces recovered from a home in Afghanistan more than a year ago, U.S. officials said.