By Amy Sawitta Lefevre and Aukkarapon Niyomyat
BANGKOK (Reuters) - Thai police launched an inquiry on Wednesday into criticism by the U.S. ambassador of a royal insult law, just a day after the junta rapped Britain's envoy for his remarks on the freedom of assembly.
U.S. Ambassador to Thailand Glyn Davies made remarks in an address on Nov. 25 at the Foreign Correspondents Club of Thailand criticizing the military government for "the lengthy and unprecedented" jail sentences handed down under the law, which exists ostensibly to protect the royal family.
Critics say the law is often used to pursue political opponents and that it has been increasingly broadly interpreted in recent years.
Thailand's military has proved sensitive to criticism from the West since seizing power in May 2014, and has drawn closer to countries such as China which have expressed support for the junta.
Davies' speech prompted a small protest outside the U.S. Embassy in Bangkok last month by a group of nationalists.
Police said a formal investigation has not been launched, but an inquiry was underway following a formal complaint.
"This matter is being investigated according to a complaint filed against the ambassador," Dejnarong Suthicharnbancha, a spokesman for the Royal Thai Police, told Reuters.
"We cannot conclude anything now and are following step by step."
Piyaphand Pingmuang, another police spokesman, said a formal investigation was unlikely.
"His Excellency the ambassador has diplomatic immunity so it is unlikely anything will proceed against him."
A U.S. Embassy spokeswoman said she could not immediately comment on the matter. The U.S. State Department in Washington said Davies was simply reiterating longstanding U.S. policy on the issue of freedom of expression.
"The U.S. government has the utmost respect for the Thai monarchy," State Department spokesman John Kirby told a briefing.
Thailand's royal insult laws are among the world's harshest and, under Article 112 of the criminal code, anyone who "defames, insults or threatens the king, queen, heir-apparent or regent" faces up to 15 years in jail.
During its 18-month rule, the military government has cracked down on perceived royal insults and handed down record jail sentences.
The investigation into the U.S. ambassador's speech follows government criticism of comments by Britain's ambassador to Thailand, Mark Kent, on Twitter.
On Monday, Kent commented on the detention of dozens of student activists who were trying to protest against alleged army corruption, saying he had hoped that the fact people were allowed to demonstrate outside the U.S. Embassy meant a relaxation on freedom of assembly.
The students were later released.
"It is disappointing that the ambassador took a position that has ended up supporting a group that has often broken the law," said deputy government spokesman Weerachon Sukhondhapatipak.
The junta has banned gatherings of more than five people and has summoned dozens of activists for questioning since taking power.
It was unclear why the junta allowed the protest outside the U.S. Embassy.
(Additional reporting by David Alexander in Washington; Editing by Andrew R.C. Marshall and Ruth Pitchford)