BANGKOK (REUTERS) - Thailand is investigating whether Amnesty International has broken any laws, its prime minister said on Friday (Nov 26), after ultra-royalists called for the human rights group to be expelled for its support of activists facing prosecution.

An ultra-royalist group sent a letter to the government on Thursday saying Amnesty's campaigns to bring an end to criminal charges against protesters calling for reforms of the monarchy had undermined national security.

More than 1,600 activists are now facing security-related charges, including at least 160 people charged under Thailand's strict laws against insulting the monarchy, which carry a potential prison term of up to 15 years.

Traditionalist Thais consider the monarchy sacrosanct and view insults to King Maha Vajiralongkorn as a threat to the fabric of society. Youth-led protests which started last year have challenged the decades-old taboos against any criticism of the king.

Asked about the royalists' request at a news conference, Prime Minister Prayuth Chan-o-cha, said: "We are checking whether there are any violations to the law and this involves the police and the interior ministry."

"If there are wrongdoings, then it (Amnesty's licence) will be revoked," he added.

Amnesty said in a statement that it has been in Thailand for several decades and will continue to work on preventing, monitoring and holding states, corporations and others accountable for human rights abuses under international law.

"We will continue to do this independently and impartially on the basis of facts," said Amnesty, which is among several human rights groups that have been vocal about the Thai government's prosecution of political activists.