BANGKOK (AFP) - Thailand's Prime Minister Prayuth Chan-Ocha on Friday said his regime would use legal, psychological and technological measures to protect the monarchy against defamation in his first official policy speech as premier.

The warning came as Amnesty International said an "unprecedented" number of people have been charged with insulting the royals since the coup, with 14 Thais indicted under the controversial lese majeste law in less than four months.

Revered King Bhumibol Adulyadej, 86, is already protected by one of the world's toughest royal defamation laws - anyone convicted of insulting the king, queen, heir or regent faces up to 15 years in prison on each count.

"We will use appropriate legal measures, psychological measures and communication technology against ill-intentioned people," General Prayuth said in a televised speech to members of the National Legislative Assembly, without elaborating on the exact methods of scrutiny.

Since seizing power on May 22, the army and junta chief - who was also appointed as prime minister last month - has emphasised his commitment to protecting the monarchy.

"The monarchy is the key pillar of our country... to create national unity," Gen Prayuth said Friday.

The King has no official political role but is seen as a unifying figure in a country that has been frequently riven by political violence, particularly since a military coup in 2006.

Last month a 28-year-old musician was sentenced to 15 years in jail for writing insulting Facebook posts about the monarchy between 2010 and 2011.

In another recent case a taxi driver was jailed for two and a half years after his passenger, a university lecturer who recorded their conversation on a mobile phone, accused him of expressing anti-royal views, Amnesty said.

Under the law anyone can make an accusation of insulting the monarchy and the police are duty-bound to investigate.

Critics say the legislation has been politicised, noting that many of those charged in recent years were linked to the "red-shirt" protest movement, which is broadly supportive of fugitive former premier Thaksin Shinawatra.

On Thursday junta spokesman Winthai Suvaree denied there had been an increase in royal defamation charges under military rule.

Gen Prayuth has said the army was forced to take control after months of protests against former premier and Thaksin's younger sister Yingluck left 28 people dead and hundreds injured, effectively paralysing her government.

But critics say the protests provided a pretext for a power grab in the latest chapter of Thailand's deep political divide.

The long-running political conflict broadly pits a Bangkok-based middle class and royalist elite, backed by parts of the military and judiciary, against rural and working-class voters loyal to Thaksin.

Thaksin was toppled in a coup in 2006 and lives in self-exile to avoid prison for a corruption conviction.