Suicide bombers killed 10 Americans and many others at a housing compounds for Westerners in the Saudi capital Riyadh, US Secretary of State Colin Powell said as he flew in for a planned visit on Tuesday.

Powell said the massive car bomb attacks in the birthplace of Islam bore the stamp of Al Qaeda and its Saudi-born leader Osama bin Laden. They came just two weeks after Washington announced it was pulling out troops from the kingdom following the defeat of Saddam Hussein in neighbouring Iraq.

"It seems we have lost 10 Americans," Powell told reporters shortly after arriving at Riyadh airport from Jordan.

Officials said at least 160 people were wounded, including 40 Americans, when cars packed with explosives were driven past armed guards at three compounds before midnight. They left a trail of rubble and mangled vehicles in their wake.

There had been warnings of new attacks on Westerners in the kingdom. Al Qaeda, blamed by Washington for the September 11 attacks, has been accused of previous bombings in pursuit of demands that non-Muslim American troops leave Saudi soil.

"Terrorism is the number-one priority of all of us and we will not rest until we have dealt with this threat to all of us," Powell said after flying in on a scheduled stop on a postwar tour of the Middle East.

"We will commit ourselves again to redouble our efforts to work closely with our Saudi friends and friends all around the world to go after Al Qaeda, to go after terrorism."

Australia said one of its citizens was also killed.

A US official, who declined to be identified, said there had been at least four bombs. Witnesses earlier said they had heard three blasts, which sent fire balls into the night sky above the Gharnata, Ishbiliya and Cordoba compounds.

Cars and pickup trucks, badly twisted and still smouldering, littered the three compounds which housed villas and four-storey blocks.

A clock in a large hall inside one building had stopped at 11:28, the time on Monday night when most witnesses said they had heard the explosions.