The move comes ahead of a planned march by ‘red shirt’ opposition protesters, who are mainly supporters of the former prime minister, Thaksin Shinawatra, and who say they plan to rally until the current coalition government calls new elections.

The red shirt movement, led by the United Front for Democracy against Dictatorship (UDD), has promised a huge but peaceful demonstration. Smaller rallies, meetings and "political schools" are being held in various provinces before convoys of vehicles are expected to carry protesters to the capital by the weekend.

Thai Prime Minister Abhisit Vejjajiva has cancelled a planned trip to Australia.

The last time the security act was invoked was during the meeting of the regional grouping ASEAN held in Thailand last October - after red shirt protests derailed an earlier attempt to host ASEAN in April.

BBC