They have asked the public, government officials and volunteers to be on alert for security threats.

The police and the Army do not have the manpower to comprehensively cover and thoroughly protect the entire city, Pinit said.

"The duty of the police is not protecting the public only but to alert the public to dangers about it and to encourage people to protect themselves," he said.

Bangkok Metropolitan Administration municipal officials are inspecting all potential risk spots - including refuse containers and mail boxes - for hidden bombs, Pinit said.

Rescue workers from the Poh Teck Tung and Ruamkatanyu foundations, public transport drivers and security guards will be trained in reporting suspicious objects or people, he added. Crime Suppression Division officers and a First Army Area troop will provide 24-hour patrols of 10 risk areas, including Suvarnabhumi Airport, bus terminals and train stations, Rajprasong intersection, Victory Monument and Chatuchak Weekend Market.

Streets with poor crime records are being checked, too. These include Chatuchak's Lat Phrao 21 and Bang Phlat's Charansanitwong 89.

An integrated police force will patrol city shopping malls and other public places, Pinit added.