A Thai court has sentenced 15 members of the "Red Shirt" political movement to four years in prison for inciting rioting that disrupted an important regional conference in 2009, a lawyer said.

The sentencing by a court in Pattaya on Thursday is the latest blow against supporters of former Prime Minister Thaksin Shinawatra, who was ousted by a military coup in 2006 after being accused of corruption and disrespect for the king.

Those sentenced included two of the group's more senior leaders, Worachai Hema, a former pro-Thaksin lawmaker, and Arisman Pongruangrong, a popular former pop singer-turned-firebrand, their lawyer Karom Polpornklang said Friday. Two of the 15 were absent for the sentencing, and the others were held after an initial denial of bail.