U.S. warns citizens of terrorist threat in Bangkok

"U.S. citizens are urged to exercise caution when visiting public areas where large groups of Western tourists gather in Bangkok," a statement on the website of the U.S. Embassy in Bangkok said.

"Foreign terrorists" may be planning attacks "in the near future," the statement said. The embassy did not provide any further information on the source of the threat.

Thailand is a highly popular tourist destination and Bangkok serves as a major transport hub for the Southeast Asian region.

Thailand has undergone periods of unrest in recent years. It experienced a spate of political violence during anti-government demonstrations in 2010.

And Muslim separatists in southern Thailand have long battled government forces in a country that is overwhelmingly Buddhist, with a number of bombings taking place last year.

The embassy said U.S. citizens should "maintain a heightened awareness when out in public," advising them to be on the lookout for unattended packages and bags in public places and other crowded areas.

It also suggested that they "keep a low profile in public areas, particularly areas frequented by foreign tourists."

Fran Townsend, a national security analyst for CNN, reported that Thai officials at one of the airports serving Bangkok were conducting pat downs and bag searches on all passengers at the departure gate for U.S. air carriers on Sunday.