The United States on Tuesday condemned Thailand's arrest of an activist's mother who allegedly insulted the royal family in a one-word Facebook post.
Patnaree Chankij, 40, was charged with violating Thailand's severe royal defamation law on Friday and could face up to 15 years in prison if convicted.
According to her lawyers, she was charged for writing "ja" -- the Thai equivalent of "yeah" -- in response to a private Facebook message critical of the royals.
Patnaree's son Sirawith Seritiwat has been a thorn in the side of Thailand's military junta since it seized power in 2014 and has himself often been jailed.
Washington, a former close ally of Thailand now increasingly exasperated by the government's antics, condemned the latest in a series of arrests.
"These actions create a climate of intimidation and self-censorship," the State Department's spokeswoman for East Asia and the Pacific, Katina Adams, said.
"We are troubled by the recent arrests of individuals in connection with online postings, and the detention of Patnaree Chankij," she said.
"The arrest and harassment of activists and their family members raise serious concerns about Thailand's adherence to its international obligation to protect freedom of expression."
Thailand's ailing 88-year-old King Bhumibol Adulyadej is the world's longest reigning monarch and revered by many Thais as a demi-god.
Anxiety over his eventual succession has helped fuel the past decade of political turmoil, which the junta claims it is seeking to resolve.
The military has become increasingly jittery ahead of an August 7 referendum on a new constitution it scripted and is determined to see pass.