Oliver Jufer, 57, was arrested on December 5 for defacing several of the king's ubiquitous portraits with spray paint during a drunken spree through the northern city of Chiang Mai, some 700 kilometres (400 miles) north of Bangkok.

 He was charged with lese majeste and destruction of public property. If convicted, he faces up to 15 years in prison, according to court officials.

 "He pleaded guilty, and the court set a date for the verdict on March 29," one court official said.

 Thailand's King Bhumibol Adulyadej is the world's longest-reigning monarch, and one of the only who is still protected by tough lese majeste charges that prohibit any insult to the royal family.

 Thai law allows anyone to file a lese majeste complaint with the police, which makes people reluctant to engage in any sort of public conversation about the king or his family.

 Jufer's alleged crime came during an especially sensitive period in Thailand, with the nation swept up in royal fever since the king's 60th anniversary on the throne in June last year. He turns 80 in December this year.

 His portrait hangs in every public building, and shrines to the king dot the sidewalks in major cities.

 Millions of Thais still wear yellow shirts to honor the king every Monday, the day of the week when he was born.

 Public concern about the king's health has run high since he underwent back surgery in July, a procedure described by doctors as a success but which forced Thais to begin to consider the delicate question of who should succeed him.

Agence France Presse