The US Ambassador to Thailand is under investigation for royal defamation over comments he made criticising lengthy jail sentences from the kingdom's lese majeste law, a foreign media group and police said Wednesday.
Under Thai law anyone convicted of insulting the king, queen, heir or regent can face up to 15 years in jail on each count.
Prosecutions have surged since the royalist army grabbed power last year, with record breaking sentences handed down in recent months to transgressors.
The Foreign Correspondent's Club of Thailand (FCCT), which represents international media inside the junta-run kingdom, said it had been asked to cooperate in the probe after US ambassador Glyn T. Davies delivered a speech there last month.
The body has been asked to assist police "in an official investigation into whether comments made by US Ambassador Glyn Davies at the club on 25 November violated article 112 of the criminal code, the lese majeste law," the club said in a statement on Wednesday.
"The FCCT is cooperating with the police," it added.
A senior Thai police source confirmed to AFP that they had received a complaint and were investigating the ambassador's comments.
In a wide-ranging talk to the FCCT, which also heaped praise on the 88-year-old Thai King Bhumibol Adulyadej, Davies expressed concern at long jail terms by military tribunals for alleged lese majeste.
"We are also concerned by the lengthy and unprecedented prison sentences handed down by Thai military courts against civilians for violating the lese majeste law," he told the FCCT audience.
"We believe no one should be jailed for peacefully expressing their views and we strongly support the ability of individuals and independent organizations to research and to report on important issues without fear of retaliation."
In Thailand any member of the public can make an allegation of royal defamation and police are duty bound to investigate -- a situation critics of the law say often results in an effective witch-hunt.
Media must heavily self censor when reporting on such cases for fear of falling foul of the law.
Ambassador Davies comments centered on criticism of the royal defamation law, not the royal family.
However in recent years the law has been increasingly broadly interpreted.
Davies spoke for more than an hour at the club on Washington's long relationship with Thailand, saying Washington respected and admired Bhumibol -- "the only monarch ever born in America".
"We think he has done so many, many wonderful things not just for Thailand but for the United States and for the region," he said.
But he added Washington was alarmed by recent convictions under the law.
Ultra-nationalists seized on his remarks and organized a small protest led by a firebrand monk outside the American embassy in Bangkok two days later.
Like all foreign envoys, ambassador Davies has diplomatic immunity so it is unlikely the probe will lead to an arrest. However Thailand can rescind his credentials at any time.
The US embassy could not be immediately reached for official comment.