A Thai court sentenced an Australian author to three years' imprisonment for insulting a member of the royal family, media reports said.

"The Nation" online said Harry Nicolaides, 41, pleaded guilty to lese majeste charges, prompting the court to reduce what was originally a six-year jail term into three years instead.

Nicolaides' novel "Verisimilitude", allegedly made critical remarks on Thailand's crown prince.

Lese majeste is a criminal offense in Thailand.

He was arrested on August 31, 2008 in Suvarnabhumi International Airport, shortly before he was to board a flight back to his country.

In an interview shortly after his arrest, Nicolaides issued a public apology.