A man suspected of involvement in the killing of an American working at a US army base in Kuwait has been extradited from Saudi Arabia, Kuwaiti security sources say.

Killed: Michael Pouliot, who worked for a US software company

The Kuwaiti is said to have entered Saudi Arabia shortly after Tuesday's ambush on two American civilian contractors, who were working at Camp Doha, the main US army base in the kingdom.

One of the Americans died and the other was seriously injured.

Kuwaiti security officials are now said to be questioning the suspect following his extradition from Saudi Arabia.

The official Saudi Press Agency said he was detained early on Wednesday near the border with Kuwait.

No group has claimed responsibility for the shooting.

Kuwaiti Prime Minister Sheikh Saad al-Abdullah al-Sabah sent a letter of condolence to US President George W Bush, describing the attack as a "terrorist act".

ATTACKS IN KUWAIT

21 Jan: Civilian US contractor killed, one wounded, in ambush on car near Camp Doha. 21 Nov: Two US soldiers wounded by policeman near Camp Doha. 14 Oct: Troops fired on from civilian vehicle near Kuwait City. No one hurt. 9 Oct: Civilian vehicle threatening US troops near Camp Doha is fired on. No one hurt. 8 Oct: US soldier killed, another wounded, by gunmen on Kuwaiti island. Attackers killed.

The US embassy in Kuwait has warned Americans to be vigilant.

The shooting happened as the men were inside their vehicle on Highway 85 near Camp Doha, north of Kuwait City.

The car had stopped at traffic lights when a gunman opened fire, police said.

The dead man, Michael Pouliot, 46, worked for a software company based in San Diego.

The other American, David Caraway, is in a stable condition in hospital with wounds in his shoulder and thigh.

Cartridge cases from rounds fired from a Kalashnikov rifle were found at the scene, according to police.

More than 15,000 US soldiers are in Kuwait in preparation for a possible war with Iraq.

There have been several attacks on US personnel in the oil-rich Gulf emirate in recent months, which have seen one soldier die and three others wounded.

While most Kuwaitis have welcomed the US troops, a minority in the country is deeply unhappy with the American presence.