BANGKOK (AFP, REUTERS) - Thai police detained leaders of an anti-junta protest on Tuesday (May 22) who had tried to mark the fourth anniversary of a coup by marching to Government House, one of the largest acts of dissent since the army grabbed power.

Protest leaders flashed a three finger salute as they were led into a police van - a resistance symbol borrowed by Thailand's anti-coup movement from the Hollywood movie "The Hunger Games".

Disquiet with the junta is simmering in Thailand, despite a ban on political gatherings since a coup toppled the elected government of Yingluck Shinawatra on May 22, 2014.

Prime Minister Prayut Chan-o-cha, who as army chief booted Yingluck's administration from power, has suggested elections will be held in February next year.

But the timetable for a return to democracy has repeatedly slipped and patience with his junta is wearing thin among many sections of Thai society.

Starting at sunrise, hundreds of student activists and middle-aged "Red Shirt" supporters of the toppled civilian government gathered to march from a university where they had camped overnight to the seat of government.

Wielding banners, Thai flags and fans with a cartoon of the premier mocked-up as "Pinocchio", they were stopped by police lines blocking their route.

Protesters intermittently tried to push up against police throughout the day.

"It is the four-year anniversary of the coup and I think now is the time to change," said Rangsiman Rome, one of the protest organisers.

Hours later after five of his co-leaders were detained by police, he and two other core organisers said they would surrender to face charges linked to violating the ban on political protest.

"I am well aware of your disappointment but it's the only way to avoid violence," he told a crowd that had held on for an hours-long standoff that included tense scuffles with police.

Around 800 policemen had been deployed to control the protest. A police vehicle was seen on Thursday afternoon moving in to take some of the group's leaders away, near the United Nations regional headquarters where some of them had gathered, before the authorities declared the protest was over.

Protesters dispersed following the detentions.

Prayut, who as army chief led the 2014 coup ending months of street protests and political gridlock, reiterated on Tuesday that there would be no election until 2019.

"I've said already that it will be according to my steps and that is early 2019 and no sooner," Prayut told reporters.

"These people have shown their point of view many times and we have taken onboard what they've said within our capacity."

The military has promised a return to democratic rule but repeatedly delayed general elections.

The junta, the National Council for Peace and Order (NCPO), said it had filed charges against five protest leaders for holding an illegal gathering.

Activists complained of a military crackdown ahead of the gathering.

On Monday, Sunai Phasuk, Thai researcher at the New York-based Human Rights Watch group, said two activists had been held incommunicado at a secret detention centre.

"Their alleged 'crime' is providing loud speakers for anti-junta rally," Sunai wrote on Twitter.

PERCEPTION CRISIS

The junta, known as the National Council for Peace and Order, is facing a public perception crisis, according to international and domestic polls that say corruption is as endemic as ever.

Deputy Prime Minister Prawit Wongsuwan defended the junta's work.

"The prime minister works hard ... the NCPO these four years has worked every day," Prawit said.

Suchada Saebae, 55, a market vendor, disagreed.

"I think the NCPO has done a rubbish job these past four years," Suchada said.

Amnesty International in a statement the NCPO had used repressive laws to target critics. "Authorities continue to flagrantly use deeply repressive laws and decrees to target human rights defenders, activists and political opponents peacefully exercising their human rights to freedom of expression association and assembly. These laws must be lifted without delay," the group said.

SHINAWATRA CLAN

Governments led by family members or their allies have dominated Thai general elections since 2001.

But they have been hit by two coups in that time and endless legal cases which have seen Yingluck and her older brother Thaksin flee abroad to avoid jail.

Prayut, who draws backing from an arch-royalist Bangkok elite, says he was forced to seize power to heal the kingdom's caustic political divides and reboot an economy stalled by months of protests against Yingluck's government.

He has banned political gatherings of five or more people and silenced criticism with legal charges and tight monitoring of prominent activists.

In between, a junta-appointed national assembly has signed off on a new constitution that ties future elected governments to a 20-year plan for the country.

The charter also creates an appointed upper house and other checks to the power of future civilian governments, in what analysts say is a brazen assault on the political base of the Shinawatras.

The family have relied on the loyalty of the rural north and north-east to power them to government - although after years put through the wringer by the army it is unclear exactly how much support the family still draws.