Nepalese authorities prevented exiled Tibetans from celebrating their spiritual leader the Dalai Lama's birthday on Wednesday over concerns that gatherings would turn anti-Chinese.
Hundreds of riot police blocked the Tibetans from entering a school on the northern edge of Katmandu where the celebrations were planned.
Only students wearing school uniforms were allowed inside the compound, while other Tibetans including many monks and nuns were stopped.
Police detained three Tibetans who tried to hold a prayer meeting on the street. A brief scuffle broke out but no one was hurt.
Tibetan gatherings in Nepal generally turn into protests against China, with participants shouting slogans demanding an end to Chinese rule in their homeland.
Laxmi Prasad Dhakal, chief government administrator of Katmandu district, issued a warning that all public celebrations were banned and police would not tolerate anti-Chinese protests.
The Dalai Lama has lived in Dharmsala, India, since he fled Tibet after a failed 1959 uprising against Chinese rule.
He is currently in Washington for an 11-day Buddhist ritual, known as a kalachakra, that organizers expect will draw upward of 10,000 followers a day from America, Asia and Europe.
His visit begins with celebrations Wednesday marking his 76th birthday.
Thousands of Tibetan exiles have been living in Nepal for the past few decades after fleeing Tibet and many more pass through Nepal on their way to India.
Nepal says it cannot allow protests on its soil against any friendly nations, including China.
Police guarded the Chinese Embassy and its visa office in Katmandu against any protests, and areas populated by Tibetans were put under heavy security.
Authorities earlier said they would allow celebrations inside monasteries provided there are no banners or slogans against China.