In the week following the coup,protesters stood in groups of four reading George Orwell’s1984. People assembling in groups of five or more are liable to be arrested on the spot.

During previous demonstrations in 2010,protesters carried coffins and dressed in black to symbolise the death of democracy,while some carried out"blood-pouring ceremonies"outside government headquarters.

“Most of these things were relatively spontaneous,” Mr Grömping said. “Apparently the blood ritual just happened out of the blue.”

Some protesters have said the three-fingered salute also represents the French revolutionary motto"liberty,equality,fraternity".

At least one woman was forced into a taxi by suspected plain-clothes police officers after making the gesture,theBangkok Post reported.

"If they gather as more than five people and show the symbol of three fingers then it's against the law,"army spokesman Winthai Suvaree told reporters.

But he suggested that people posting photos on the internet were unlikely to be detained,saying coup makers were"not paying any attention"to the three-finger salute.

Mr Grömping said while benign forms of protest may be tolerated in the well-connected capital of Bangkok,where media coverage is focused,there is less scrutiny and protection in other parts of the country.

“What happens in the north-east and the north … we don’t know what’s going on,” he said.

- with agencies