The US Secretary of State, Colin Powell, has warned of the dangerous situation which is developing inside Saudi Arabia.
In further violence over the weekend, an American citizen was kidnapped and another was killed by suspected al-Qaeda militants.
Mr Powell was speaking after an Islamist website carried a statement purportedly from the group which claimed responsibility for the recent violence in Riyadh.
Yesterday, the US urged its citizens to leave the kingdom, while Britain is allowing home all non-essential diplomatic staff in Saudi Arabia.
