BANGKOK (AP) — The U.S. said Friday it is disappointed Thailand has charged an American citizen with insulting the country’s monarchy, a severe offense that carries a penalty of up to 15 years in prison.

Joe Gordon allegedly translated parts of an unauthorized biography of King Bhumibol Adulyadej and posted articles online that were deemed to have defamed the royal family.

Gordon was formally charged Thursday after being arrested in May and detained for the maximum 84 days that a suspect can be held without charge.

The American has denied the charges, according to the Thai-language prachatai.com news website, which tracks cases of lese majeste, as the crime of insulting the monarchy is known.

The 54-year-old Thai-born man lived in the U.S. state of Colorado for about 30 years before returning recently to Thailand, the website said.

Thailand is a constitutional monarchy but has severe lese majeste laws that mandate a jail term of three to 15 years for any person who “defames, insults or threatens the king, the queen, the heir to the throne or the Regent.”

U.S. Embassy spokeswoman Kristin Kneedler said the U.S. has urged Thai authorities to respect freedom of expression and “was disappointed” with the charges against Gordon.

Embassy officials have had regular contact with Gordon, she said.