Thai students charged with royal defamation law ahead of demonstration

The three-finger protest gesture is flashed during a student rally in Bangkok (Sakchai Lalit/AP)

Thai authorities have escalated their legal battle against the students leading pro-democracy demonstrations by charging 12 with violating a harsh law against defaming the monarchy.

It comes as the Thai capital Bangkok girded for another rally as the students push their demands that prime minister Prayuth Chan-ocha and his government step down, the constitution be amended to make it more democratic and the monarchy be reformed to be made more accountable.