The United States and Britain said on Tuesday they were closing their embassies and other missions in Saudi Arabia on Wednesday due to the risk of attacks following suicide bombings in Riyadh last week.

The moves came a day after Saudi Arabia's ambassador to Washington, Prince Bandar bin Sultan, said he believed the suicide bombers who struck in Riyadh were planning a much bigger operation.

"In response to information that some strikes may be imminent, the (Riyadh) embassy and consulates general in Jeddah and Dhahran will be closed on May 21, 2003," the US embassy said in a statement. It said they would not reopen before Sunday.

The statement gave no further details and Saudi officials were not immediately available for comment.

US and Saudi officials have blamed the bombings on al Qaeda militants led by Saudi-born Osama bin Laden. The United States has accused bin Laden and al Qaeda for the September 11, 2001 hijacked airliner attacks on US cities.

The British Foreign Office said it would close its embassy and two other offices in Saudi Arabia from Wednesday.

"We have received credible information that further terrorist attacks against unspecified targets in Saudi Arabia are being planned and may take place imminently," a Foreign Office spokeswoman said in London. "The embassy in Riyadh, the consulate in Jeddah and the trade office in al-Khobar will be closed to the public from tomorrow."

The spokeswoman said the situation would be kept under review but it was planned to reopen the embassy and offices on Saturday. At this stage, it was intended that staff would continue to work from the buildings.

Prince Bandar said Saudi and US intelligence had picked up '(electronic) chatter' that terror groups were possibly planning further attacks.

Saudi Arabia, the birthplace of Islam, said it was stepping up measures to prevent attacks after the Riyadh blasts, which killed at least 34 people, including eight Americans.

The triple attacks at foreign residential compounds were the first time civilians were targeted in the kingdom.

The US embassy statement followed the arrest of a Saudi gunman who was roaming around the US consulate in Dhahran. The gunman did not fire any shots and the Saudi authorities described him as 'mentally disturbed'.