No level of security can guarantee protection against attacks by terrorists willing to die for their cause, the Saudi ambassador to the United States said Thursday.

"But what we can do, however, is pursue them vigorously and when we get them, we bring them to justice, try them and punish them swiftly and harshly," said Prince Bandar bin Sultan (search).

Bandar once again defended his country's response to a request by the United States for improved security in an area of Riyadh where Westerners live. Speculation about security arrangements there continues in the wake of the car-bomb attacks early this week that killed over 30 people, including several Americans.

Leading congressional figures on intelligence issues said Wednesday the attacks would have been difficult to stop even if Saudi officials had responded more aggressively to U.S. pleas.

U.S. ambassador Robert Jordan (search) said that before the attacks, Saudi officials failed to respond to repeated requests for more protection at Western residential compounds and government installations.

Bandar acknowledged that Wednesday in a series of U.S. television interviews. But he suggested that Jordan sought security for only one compound — and that Saudi security successfully protected foreigners there.

"He asked for increased security at a certain compound," 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."

"Our security agencies, ... the air force came to the conclusion there were adequate measures there," he said Thursday on ABC's Good Morning America.

But Bandar quickly added: "There is no 100 percent security when a determined, crazy, evil person is determined to die."

Traveling with Secretary of State Colin Powell in Europe, a senior U.S. official said it was up to the companies involved and to the Saudi government to act on requests for additional security.

"We are in a position to recommend special assistance," he told reporters, but it was not clear whether the request involved all three facilities bombed by the terrorists.

The official, speaking on condition of anonymity, said there are dozens of housing complexes spread through the kingdom, and they simply are not as secure as U.S. Embassies.

The top Democrat on the Senate Intelligence Committee, Sen. Jay Rockefeller (search) of West Virginia, said additional security might not have stopped the attacks.

In the past, he said, Al Qaeda "would have a guy with a gun in a truck trying to break through a barrier and do it all himself. Here they did it differently. They had people with guns go in shoot the security" then detonate the bombs.

"It's a big adjustment," he said. "It's them figuring out how to do things more efficiently."

A U.S. counterterrorism official said it wasn't surprising that gunmen would shoot guards before rolling in a car bomb. But the official, speaking on condition of anonymity, said Al Qaeda had never hit a civilian residential area before.

Senate Intelligence Committee Chairman Pat Roberts, R-Kan., said such areas are difficult to protect.

"If you look at the car bombs, they were extremely powerful and you would have to have very, very tough security at levels that probably you would not foresee," he said.

A State Department official said U.S. and Saudi officials would look at how security issues were handled in the days before the explosion.

A six-member FBI team was expected to arrive in the kingdom Thursday to assist in the investigation. 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 killed 19 U.S. service members.

Current and former officials said the relationship between Saudi police and U.S. investigators has improved since then.

Saudi officials have 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 them 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.