Around 50 Red Shirt supporters threw bottles and stones at an estimated 200 Yellow Shirts in front of the police Crime Suppression Division offices, the Bangkok Post reported.
The groups gathered after police summoned for questioning a former female teacher who publicly accused a Red Shirt supporter, Darunee Kritbunyalai, of defaming the royal institution last month.
The Red Shirts are in the main supporters of the United Front for Democracy against Dictatorship, a mostly rural-based party, and back the ruling Pheu Thai Party. Yingluck Shinawatra led the PTP to a landslide victory in July 2011 and became Thailand's first woman prime minister.
Yellow Shirts are mostly royalists, ultra-nationalists and the urban middle class who support the People's Alliance for Democracy.
The Red Shirts were protesting the scheduled appearance of the teacher at the police station. The appearance was postponed to late October because of the demonstration, the Post reported.
A truck was damaged but police made no arrests.
However, such confrontations can get out of control, Thawee Surarittikul, a political analyst at Sukhothai Thammathirat Open University, told the Post.
"Both sides are waiting for an issue which could be a trigger point leading to a bigger protest," Thawee said.
"Any controversial or sensitive issue picked up on by either side could possibly spark a swarming effect," he said.
Thailand's lese-majeste laws protect the king of Thailand, as head of state, from criticism, although his immediate political power is limited.
King Bhumibol Adulyadej, 84, has reigned since 1946, nearly six years longer than the world's second-longest reigning monarch, Queen Elizabeth II of Britain.
The laws have been heavily criticized as a tool for the government, police and military to clamp down on political dissidents.
But foreigners have been caught out by lese-majeste, including U.S. citizen Joe Gordon who was picked up by Thai authorities while on a visit to the country last year.
He was sentenced in November to five years in jail for translating parts of a banned biography of the king and posting them online.
Gordon, a 55-year-old, Thai-born U.S. citizen, had lived in the United States for 30 years and had posted the offending content online while living in Colorado.
In July Gordon received a royal pardon from the king and was freed.
Thai citizens have suffered much harsher sentences under the law, including Ampol Tangnoppakul, 61, who died in custody in May.
He had been sentenced to 20 years in prison for sending text messages that allegedly defamed Queen Sirikit.
The Red Shirts wanted an investigation into his death which they suspected was due to a lack of medical attention, the Post reported at the time.
Ampol's sentence prompted the United Nations to call for Thailand to review the lese-majeste law with an eye to allowing more freedom of speech.
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