Bangkok
Authorities had set up a large barricade of shipping containers and barbed wire to block protesters from getting near the palace on Saturday, dpa news agency reported.
The rally was largely peaceful, with demonstrators earlier flying kites spray-painted with images of jailed pro-democracy protest leaders, although tensions escalated when protesters removed the containers blocking their path to the Grand Palace later in the day.
"The police officers will remain in the area until peace and order has truly been restored," police spokesperson Krissana Pattanacharoen said, adding that at least five protesters had been arrested.
At least 11 people were hurt during the clashes, the city's Erawan Emergency Medical Centre said.
The rally was organised by the REDEM (Restart Democracy) Group, made up of young demonstrators calling for reforms to the monarchy and demanding the military-approved constitution be rewritten.
Protests led by young people have stalled partly due to the country's surging coronavirus caseload, although a recent mass trial for pro-democracy leaders charged with sedition and lese-majesty has prompted protesters back on the streets.
Thailand's lese-majesty law can mean up to 15 years in prison if offenders are found guilty of insulting the king, queen, heir or regent.
Authorities have charged more than 60 people under the law since November, according to rights group Thai Lawyers for Human Rights.
The current Thai government was elected in 2019.
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