The case sparked US criticism of its south-east Asian ally, and called for the country to respect freedom of expression.

Thai-born Lerpong Wichaikhammat, 55, also known as Joe Gordon, had pled guilty to using the internet to spread information that insulted the monarchy, charges stemming from material posted on his blog in the United States.

"Joe Gordon was granted a royal pardon and released on Tuesday," Walter Braunohler, a spokesman at the US embassy in Bangkok, said.

The case highlighted Thailand's extensive use of the world's most draconian laws to stamp out even the faintest criticism of 84-year-old King Bhumibol Adulyadej.