Numerous people were wounded when bombs exploded at Westerners' compounds in Riyadh overnight - hours before US Secretary of State Colin Powell was due to arrive in the Saudi capital, witnesses said on Tuesday.
"We heard a huge noise and we saw many ambulances coming and gathering victims," a witness near one compound told Reuters.
The Saudi Interior Ministry said in a brief statement there were three explosions and authorities were investigating.
Diplomatic sources in the Jordanian capital, Amman, where Mr Powell was spending the night, said three compounds had been hit and unconfirmed reports said most residents were Americans.
The sources had no information on injuries at the three locations which they named as Cordoval, Gedawal and the Hamra.
Mr Powell plans to leave Amman for Riyadh tomorrow morning as part of a Middle East tour. It was not immediately clear if the incidents would affect his travel plans.
Suspected militant Islamists have twice launched major attacks on US targets in Saudi Arabia since the 1991 Gulf War.
In November 1995, five Americans and two Indians were killed and 60 people injured in an explosion in a car park near a US-run military training centre in Riyadh.