Five companies of police and about 100 mobile police have been deployed in the northern province of Chiang Mai to uphold security and order during the anti-government rally on Sunday, a local media reported.

The Commander of the Chiang Mai Provincial Police, Pol Maj Gen Sommai Kongwisaisuk, said security checkpoints were set up in every district of Chiang Mai.

The United Front for Democracy against Dictatorship (UDD), also known as red-shirt movement, has staged demonstration in capital city of Bangkok and Chiang Mai on Sept. 17-19 with smaller rallies in other provinces to mark the fourth anniversary of the 2006 coup detat.

Pol Maj Gen Sommai said the police were not very worried after the group announced that there would be no guards during their rally. If "red-shirt" guards are around, it is likely that there will be a third party with ill-intention in the gathering, he said.

However, he asked the public to inform the authorities if they witness any unusual activity.

During the months-long protest of the UDD from March to May this year, the "red-shirt" protesters deployed black-clad guards to protect themselves. But there were also men in black armed with munitions lurking among the protesters and attacking against troops and civilians. The government blamed these black-clad men for triggering clashes between the military and the protesters which eventually resulted in 91 deaths and almost 2,000 injuries.