Facing accusations of failing to rein in those suspected of links with al-Qaida, Abd Allah on Thursday urged citizens to help security forces combat a “misguided, deviant group of terrorists”.

There have been several bloody clashes with Saudi security forces and wanted people which left at least 16 suspects and 11 Saudi policemen killed.

The Crown Prince’s remarks came a day after the State Department warned its citizens not to travel to Riyadh, saying it had information about threats aimed at American and Western interests, including civil aviation.

Earlier on Wednesday, Britain also said it had intelligence on security threats to British aviation interests in Saudi Arabia. British Airways announced it was suspending flights to the kingdom.

US officials said documents found this week in Riyadh apparently indicated that the King Khalid airport had been under surveillance.

Washington had already warned US citizens against nonessential travel to Saudi Arabia, following the bombing of a residential compounds in Riyadh that killed 35 people.