Thousands of protesters staged another anti-government rally in the Thai capital, Bangkok, on Sunday to demand political reforms.
Demonstrators want a revised constitution and are also calling for reform of the monarchy – a sensitive subject in Thailand.
Under Thai law, anyone criticising the royal family faces long prison sentences.
There have been almost daily student-led demonstrations in recent weeks.
Several protest leaders have been arrested.
But organisers said they hoped Sunday’s rally would show broader support for change beyond the student groups. Bangkok police said on Sunday evening that about 10,000 attended the protest.
“We want a new election and a new parliament from the people,” 24-year-old student activist Patsalawalee Tanakitwiboonpon told the cheering crowd.
“Lastly, our dream is to have a monarchy which is truly under the constitution.”
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They waved banners and chanted: “Down with dictatorship, long live democracy.”
The protesters are demanding that Mr Prayuth – a former general who won disputed elections last year – stand down.
The BBC’s Jonathan Head in Bangkok says recent inclusion of the monarchy in the protesters’ demands has electrified the debate.
About 600 police officers were monitoring the protest.
Nearby, dozens of supporters of the monarchy also staged a rally.
Last year’s elections were the first since the military seized power in 2014 and for many young people they were seen as an opportunity for change.
But the military had taken steps to entrench its political role, and the election saw Mr Prayuth re-installed.
Mr Prayuth says the majority of Thais do not support the protesters.
The latest wave of protests began in February after the pro-democracy Future Forward Party (FFP) was dissolved by court order.
Protests were held, but were quickly halted by Covid-19 restrictions.
Tensions increased in June when Wanchalearm Satsaksit, a prominent activist who had been living in Cambodia in exile since 2014, went missing. The Thai government has denied any involvement in his disappearance.
Student-led protests erupted again on 18 July, despite a ban of mass gatherings under the country’s state of emergency. Rallies have been held almost daily since then.
Last week, prominent student leader Parit Chiwarak, 22, was arrested and faces charges including sedition, assault and holding an event that could spread a disease.