Riyadh, Saudi Arabia — The United States will close its missions in Saudi Arabia on Saturday for an undetermined period because of "credible" information that terrorists are about to carry out attacks, the U.S. Embassy said Friday.

The Canadian embassy will remain open, however, a Foreign Affairs spokeswoman said.

The United States also warned that Taliban insurgents in Afghanistan may attempt to kidnap American journalists working in that country.

The U.S. Embassy in the Saudi capital, Riyadh, said Americans in the kingdom should be "vigilant when in any area that is perceived to be American or Western."

The embassy said in a warden message on its website that the missions in Riyadh, Jiddah and Dhahran would close to assess their "security posture."

They will then advise the American community when the review is completed and when the missions plan to resume normal operations.

The embassy said it had received "credible information that terrorists in Saudi Arabia have moved from the planning to operational phase of planned attacks in the kingdom."

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She said her department would continue to evaluate the security situation in the kingdom. Canadians have been advised against travelling to Saudi Arabia and those who remain are urged to exercise extreme caution and keep in touch with the embassy or its wardens.

On Monday, Saudi police uncovered a cell believed linked to al-Qaida network in the holy city of Mecca. Police believe the cell had planned to carry out attacks during Ramadan.