Saudi officials say they have discovered large amounts of bomb-making materials in a militant hideout south of Riyadh.

They say the cache included more than 2,000 kilograms of chemicals that could be used in bombs. 

News of the discovery came hours after the U.S. Embassy in Riyadh warned Wednesday that it had indications of "operational planning" for terrorist attacks in Saudi Arabia.  It urged Americans to exercise caution and be vigilant.

The embassy said it did not have specific information about the timing, targets or method of attack.

Al-Qaida-linked militants have been blamed for a number of terrorist attacks in Saudi Arabia since May 2003.  Many of those attacks have targeted Westerners.

Some information for this report provided by AP, Reuters.