A suspect arrested in Saudi Arabia in the shooting of two Americans in Kuwait was not working alone, a Kuwaiti security officer said Thursday.

The official, speaking on condition of anonymity, said the man arrested in Saudi Arabia Wednesday was now in Kuwait and being interrogated. The official identified the suspect as Sami al-Mutairi, a civil servant in his 20s, and said he was the prime suspect, but he "had partners, maybe two."

The Saudi Press Agency had said border guards arrested the suspect early Wednesday and "the initial investigation revealed that he was the assailant who fired on the American citizens." One of the Americans was killed.

John Moran, spokesman for the U.S. Embassy said, said the United States hoped "the investigation will move rapidly to apprehend those responsible for this crime and determine if they have ties to any larger organization. We call on the government to do everything in its power to protect our citizens from terrorist attack and to prevent any further tragedies."

The shooting was the first assault on U.S. civilians in Kuwait and the third on Americans since October in the oil-rich emirate, where pro-American sentiment is usually strong and where thousands of U.S. troops are assembling ahead of a possible war on Iraq.

The U.S. Embassy said it was urging Americans to be alert to their surroundings. About 8,000 American civilians live in Kuwait, in addition to 17,000 personnel stationed at the main U.S. military based here and thousands of other troops who come for regular exercises.

In Tuesday's attack, a gunman hiding behind a hedge ambushed the sport utility vehicle carrying two civilian contractors working for the U.S. military, killing one and critically wounding the other. The attack took place at a stop light about 3 miles from the U.S. military's Camp Doha, which is 10 miles west of Kuwait City.

One of them, David Caraway, was in stable condition Wednesday at al-Razi hospital in Kuwait City. His co-worker Michael Rene Pouliot, 46, was killed.

Nobody has claimed responsibility for the attack.

A wreath-laying ceremony was planned Thursday at the intersection where the shooting took place, to be followed by a private memorial service on the military base where the two victims worked.

Kuwait's crown prince and prime minister, Sheik Saad Al Abdullah Al Sabah, sent letters of condolences to President Bush condemning the "terrorist act," the state-run Kuwait News Agency said.

Small, oil-rich Kuwait was liberated in 1991 from a seven-month Iraqi occupation by a U.S.-led coalition, and depends on Washington for protection. As U.S. forces pour into the emirate, it could become a launch pad for any war on Iraq.

On Oct. 8, two Kuwaiti Muslim fundamentalists opened fire on Marines taking a break from war games on the island of Failaka, killing one and injuring another. Other Marines killed the assailants, who reportedly had links to the Al Qaeda terror network blamed for the Sept. 11, 2001 attacks on the United States. A policeman later described as "mentally unstable" also shot at two U.S. soldiers in their civilian car on a highway on Nov. 21.

Kuwaiti officials have described the attacks as isolated incidents, distancing themselves from any deeper Al Qaeda presence. Scores of Kuwaitis have fought with Muslim extremists in Afghanistan, Chechnya and Bosnia.