The United States said last night that guerrillas were close to carrying out attacks in Saudi Arabia and that US diplomatic missions in the Gulf Arab state would close on today to review the security situation.
The warning by the US embassy followed Saudi security raids on Thursday in which three militants suspected of links to Saudi-born Osama bin Laden's al Qaeda network were killed.
The embassy, which was closed for the Muslim weekend on yesterday, urged the 40,000 Americans in the kingdom to be vigilant when in areas perceived to be American or Western.
Britain said it was reviewing security but had no plans to close its embassy in Riyadh.
Britain last month dramatically raised its warning against travel to Saudi Arabia, saying militants may be in the final phases of planning attacks.