Ambassador Robert Jordan said the United States sought in vain before Monday to get security tightened around Western residential compounds in the Saudi capital amid warnings of possible attacks.
"As soon as we learned of this particular threat information, we contacted the Saudi government," Jordan said on CBS News' "The Early Show" Wednesday. "We continue to work with the Saudis on this, but they did not, as of the time of this tragic event, provide the additional security we requested."
Foreign Minister Prince Saud al-Faisal told reporters he had "not heard of this" but said the Saudi government has always fulfilled any requests by the American or other embassies for additional security.
However, he admitted there were security lapses, saying Saudis should "look within themselves and see whether we have done enough to preserve the security of our nation."
Asked whether that was an admission of security failures, Saud said: "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."
In the latest anti-Westerner attacks, bombers on a motorcycle set off a series of explosions Thursday at six U.S.-based Shell gas stations in southern Karachi, police said. There were no injuries.
Over the course of three hours, two men on a motorcycle went from one Shell station to the next, got gas and placed the home-made devices in a garbage can, Police spokesman Malik Sheikh said.
Monday night's bombings targeted three residential compounds where expatriate executives and professionals live, killing 34 people — including eight Americans and nine of the attackers — and injuring nearly 200.
Saud said the attacks, blamed on Osama bin Laden's al Qaeda terror network, were designed to drive away foreigners, but he insisted Saudi Arabia is safer now than before the car bombings.
Still, some foreigners were going ahead with plans to leave.
"I'm terrified and I'm really scared. I think we need a break from all of this," said Tanya Scott, a 36-year-old Australian flight attendant.
The U.S. Embassy was closed for security reasons Wednesday and the State Department ordered home nonessential diplomats and family members.
Saudi officials, stung by criticism that they did too little to combat militancy ahead of the Sept. 11 attacks, have taken pains to show unusual openness and determination in the wake of Monday's attacks.
Crown Prince Abdullah went on national television Tuesday, vowing to "put an end" to those behind the attacks.
Along with reassuring foreign business, the kingdom's leadership is eager to see that the attacks do not strain ties with Washington, where some blame the kingdom's strict version of Islam for breeding the likes of Saudi-born bin Laden and the Sept. 11 hijackers.
The attacks came as the United States was withdrawing most of its 5,000 troops from Saudi Arabia, a presence bin Laden has used as a pretext for attacks.
"Saudi Arabia must deal with the fact it has terrorists inside its own country," White House spokesman Ari Fleischer said. "Their presence is as much a threat to Saudi Arabia as it is to Americans."
But Fleischer insisted the U.S.-Saudi relationship is not being reassessed as a result.
"The one thing the terrorists want more than anything else is to be able to attack the United States, to attack others in the region and force us into changes in our policies," he said. "That will not happen."
The Saudi foreign minister echoed that sentiment, saying countries who are terror victims "feel sympathy for each other."
Prince Saud said 15 terrorists took part in the Riyadh attacks; at least nine were killed, but some are presumed to have gotten away.
"Ironically it was 15 Saudis who did what they did in America and 15 Saudis who did what they did in Saudi Arabia," he said. Of the Sept. 11 hijackers, 15 were Saudi and four were from other Arab countries.
"Certainly it goes to the heart of the argument that nobody could accuse us of being responsible for attacking our country," Saud added.
FBI agents were not expected to arrive in Saudi Arabia to join the investigation until Thursday at the earliest. Officials say every day lost in getting to the crime scene makes the job of finding the terrorists that much harder.
The Saudi government has said the attacks are connected to 19 al Qaeda operatives who engaged in a gunfight with police in Riyadh on May 6 and escaped, though one later surrendered. Interior Minister Prince Nayef said the 19 are believed to take orders directly from bin Laden.
Besides the eight Americans, those killed Monday were seven Saudis, three Filipinos, two Jordanians, and one each from Australia, Britain, Ireland, Lebanon and Switzerland, according to the Interior Ministry.