BANGKOK - Thai police arrested activist lawyer Anon Nampa on Wednesday over an Aug. 3 protest at which he called for reform of the powerful monarchy, the second time he has been arrested this month, a police officer said.

Anon, 36, has been at the forefront of a movement that has staged protests almost daily for the past month in the Southeast Asian country. He was the first to call openly for changes to King Maha Vajiralongkorn's role, breaking a longstanding taboo.

Anon had been charged with sedition, said the officer, who declined to be named because he was not authorised to speak to media. He did not give further details. Neither Anon, who already has several other cases pending against him, nor his lawyer were available for comment.

Police said earlier they had warrants for Anon and five other activists. They had all been at an event where a call was made for reforms to the monarchy as well as broader demands for a new constitution and elections and an end to the harassment of government opponents.

Prime Minister Prayuth Chan-ocha, a former junta leader who rejects activists' accusations that last year's election was manipulated to keep him in power, said he acknowledged student demands but they should not touch the monarchy.

"There are 67 million Thais," Prayuth told reporters. "I believe the majority do not agree with the protesters."

Demonstrators challenging the monarchy say greater democracy is impossible without changes that would limit the king's constitutional role in a country that has had 13 successful coups since absolute monarchy ended in 1932.

The Royal Palace has not responded to the demands.

Insulting the monarchy can lead to a 15-year jail sentence, but Prayuth has said the king had requested no prosecutions under the lese majeste laws for now. Sedition carries a term of up to seven years.

The protest movement drew 10,000 people to the biggest demonstration in years in Bangkok on Sunday, and this week some high school pupils have joined protests that started on university campuses.

Hundreds of Thai high school students rallied at the education ministry on Wednesday and gave three-finger "Hunger Games" salutes in support of an anti-government protests and to demand more freedom in schools.

Many also wore white ribbons to show their support.

Meanwhile, the Ministry of Digital Economy and Society had filed a cybercrime complaint against exiled academic Pavin Chachavalpongpun for creating a Facebook group deemed critical of the monarchy, a spokesman said.

The group, called Royalist Marketplace, has more than one million members.

The ministry said it acted after Facebook had not acted on its request to shut the group down.

"The ministry's action is the crudest form of information censorship. It goes against the freedom of expression that we are all entitled to," Pavin told Reuters.

In Bangkok, some 200 Thai rightists set up a group to oppose the anti-government protesters. So far, counter protests have drawn only a few dozen people. REUTERS