Hundreds of Buddhist monks led elephants through Bangkok to demand that Thailand's new post-coup constitution enshrine Buddhism as the national religion.
Elephants, considered sacred by many Buddhists, are often used in Thai religious ceremonies.
Police had hoped to persuade the monks, who were joined by hundreds of supporters, to leave the elephants at the city limits as they marched into the capital, said Bangkok Police Commissioner Lt. Gen. Adisorn Nontree.
But protesters pushed their way through a police line as they entered Bangkok, briefly scuffling with police. Marchers planned to meet up with protesters at Bangkok's parliament building.
Police said they feared the elephants would make the rally difficult to control, and that the scorching sun would make Bangkok's streets too hot for the animals to walk on.
The march came a day after coup leader Gen. Sonthi Boonyaratglin backed the idea of recognizing Buddhism as the national religion, amid a worsening Islamic insurgency in the south.
The uprising has killed more than 2,000 people since it flared in 2004. More than 90 percent of Thailand's 64 million people are Buddhists, and Muslims who form the majority in the deep south have long complained of discrimination.
The first draft of a new post-coup constitution, made public last week, retains the wording on the topic from Thailand's previous constitution, from 1997. It does not name Buddhism as the national religion, and says the state will protect all faiths.
However, Sonthi said he expected the charter's drafting committee to "review its decision on this issue," The Bangkok Post newspaper reported Wednesday.
"If a stipulation in the charter to this effect leads to peace in the country, then it is better that it is included. Those who say there is no need for such a stipulation don't take the issue that seriously," the newspaper quoted Sonthi as saying.
Sonthi also recommended adding a clause requiring the government to "take care of other religions, including Christianity and Islam."
Wednesday's protest was the latest in a series of demonstrations by monks. It revives a debate dating back to 1997, when a campaign to make Buddhism the national religion was dropped amid concerns that it would divide the country.
Thailand's 1997 constitution was scrapped after a September 19 coup that ousted then-leader Thaksin Shinawatra.
Coup leaders appointed a committee to draft a new constitution that is expected to be put to voters in a referendum as early as September, ahead of elections scheduled for the end of the year.