Thai police fired rubber bullets Friday in clashes with dozens of protesters trying to march to the venue of an Asia-Pacific summit in Bangkok.
Around 50 people demonstrating against the event and Prime Minister Prayut Chan-o-Cha threw rocks, bottles and broken glass during half an hour of scuffles with hundreds of riot police.
The incident took place near the Thai capital's Democracy Monument, around eight kilometres (five miles) from the conference hall where Prayut was hosting US Vice President Kamala Harris and other leaders from the Asia-Pacific Economic Cooperation (APEC) forum.
The drama kicked off when protesters barbecued chillies on a police car and billowed the spicy smoke towards the riot squad.
Police said 25 people have been arrested on charges of assault, vandalism, arson and obstructing officers.
Ten people suffered minor injuries in the afternoon clash, according to the Erawan Medical Centre.
"We weren't able to control the situation, that is why the use of force was necessary," Royal Thai Police Major General Archayon Kraithong told reporters in Bangkok.
Authorities have erected shipping containers to block the path of protesters near the monument.
Around 28,000 police have been deployed to secure the APEC summit, which is also being attended by Chinese President Xi Jinping and leaders from Japan, South Korea, Canada and Australia.
Former coup leader Prayut is deeply unpopular in Thailand and in 2020 there were mass youth-led pro-democracy street rallies attracting tens of thousands at the peak, calling for his resignation.
He is due to face voters at an election in the coming months.