Thai police have arrested a man they say posted messages and photos on Facebook that insulted the king, adding to the skyrocketing number of lese majeste cases in the country.

Thailand's lese majeste law is the world's harshest, mandating long prison sentences for anyone who defames, insults or threatens the monarchy. The charges have often been used to harass political enemies.

National police spokesman Lt. Gen. Prawut Thawornsiri said Wednesday that 47-year-old Pongsak Sribunpheng broke the lese majeste law and a related computer crime law by posting the insulting Facebook content in 2012.

Prawut said Pongsak confessed to the crimes and said he took part in the Red Shirt political movement. The Red Shirts were allied with the former Thai government, which was ousted by a military coup last year.