Five Thai students were detained Wednesday after flashing the three-finger salute from "The Hunger Games" films during a speech by the premier, officials said, in the latest crackdown on opposition to May's coup.

The students brandished the gesture, an unofficial symbol of resistance against the military regime, as Prime Minister Prayut Chan-O-Cha delivered a speech on his first official visit to the northeastern province of Khon Kaen, a stronghold of the opposition "Red Shirt" street movement.

Officials removed the students from the venue after they whipped off sweaters to reveal T-shirts displaying Thai letters spelling out "No Coup" and flashed the three-fingered salute, according to public broadcaster Thai PBS.

"We handed over the five students to army officials," Jitjaroon Srivanit, commander of Khon Kaen provincial police, told AFP.

A military official, who did not want to be named, confirmed that the students had been detained.

"They have been taken to a military camp," he said.

Political assemblies of more than five people were banned under martial law declared by then-army chief Prayut two days before he ousted the kingdom's caretaker government on May 22.

Prayut, who is head of the ruling junta and prime minister, retired as army chief in September.

Since seizing power the military has suspended democracy and curtailed freedom of expression in the kingdom, responding aggressively to any form of protest.

In June police arrested a lone student reading George Orwell's anti-authoritarian novel "Nineteen Eighty-Four" and eating a sandwich, while others have previously been detained for displaying the three-fingered salute.

Deputy government spokesman Sunsern Kaewkumnerd said Prayut was "unaffected" by the incident "because they are youth".

"People can think differently but should not quarrel with each other," Sunsern said.

Sasinan Thamnithinan, a human rights lawyer, said that in return for their release the students had been asked to sign undertakings not to engage in political activity -- on threat of expulsion from the law faculty at Khon Kaen University, where they study.

It was not immediately clear if the five were later released.

The military claims it was forced to seize power in Thailand after nearly seven months of political street protests which left nearly 30 people dead and hundreds of others wounded.

But critics accuse the junta of using the unrest as a pretext to curb the political dominance of fugitive former premier Thaksin Shinawatra and his allies, who have won every election in more than a decade.

Thailand's 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 -- many of whom are part of the Red Shirt movement -- loyal to Thaksin.

Khon Kaen is in the Red Shirt heartland of northern Thailand where Thaksin is broadly admired for his pro-poor policies.