Riot police stand in formation outside the Centre for Maintaining Peace and Order on the outskirts of Bangkok.
Nine people have died and hundreds have been injured since anti-government demonstrations started in November.
Prime Minister Yingluck Shinawatra remains determined to go ahead with a general election on February 2. There are now fears pro-government redshirts could once more take to the streets to defend her rule, in a reprise of 2010 unrest which saw 90 people killed.
Paul Chambers, a researcher at at Payap University in Chiang Mai, warned the elections –which Ms Yingluck is expected to win – could spark further turmoil if the election commission chooses not to endorse the result.
Military chief Prayuth Chanocha has not come forward to support the government’s position, leaving open the possibility that the army could side with protesters.
‘‘The situation is truly bizarre,’’ Dr Chambers said. ‘‘It’s like a slowmotion coup.’’