Nepalese police arrested 18 people in Kathmandu on suspicion of "anti-China activities" on Sunday, the anniversary of the 1959 rebellion against China's rule in Tibet.
"Some of the people we arrested were Tibetan but we have not interrogated all of them yet," police spokesman Uttam Subedi told AFP, saying all but three had been released on the same day.
Nepal, home to around 20,000 Tibetans, is under intense pressure from Beijing over the exiles, and has repeatedly said it will not tolerate what it calls "anti-China activities".
On February 13 a Tibetan monk doused himself in petrol in a Kathmandu restaurant and set himself on fire, becoming the 100th self-immolation bid in a wave of protests against Chinese rule since 2009.
The gruesome burnings, most of which have occurred in Tibetan-inhabited areas of China, are seen as a sign of desperation in the community over perceived religious and political persecution in Chinese-ruled Tibet.
In the lead-up to Sunday's 54th anniversary of the Tibet uprising, the Nepal government re-exerted its security efforts.
Home ministry spokesman Shanker Koirala told local journalists last week that the government was making "necessary security arrangements in areas deemed sensitive, to foil any untoward incidents".
In a statement released on Sunday, Prime Minister of the India-based Tibetan Government in Exile, Lobsang Sangay, condemned the lack of political freedom inside Tibet.
He said when people speak out they "risk prolonged imprisonment, torture, public humiliation and disappearance at the hands of security forces".
"The prohibition of peaceful protest and harsh punishments compel Tibetans to resort to self-immolation", he said.
Tibetan activists in Kathmandu said they had been sent a letter by the chief of Kathmandu's district administration asking them to cancel public observance of the March 10 anniversary.
"We received a letter asking us not to observe the anniversary. So we decided not to organise it this year," said a Tibetan exile who identified himself as Sonam.
A Tibetan activist in Kathmandu who spoke on the condition of anonymity said: "We see how intense the pressure is from the government and we don't want to just hand ourselves to the police for no reason."
He said high bail costs were an added disincentive in situations where arrest was imminent.
The district administration chief would neither confirm nor deny the letter, but told AFP he gave the Tibetans a verbal warning last week against organising a protest "because activities against China violate Nepal's law".
Activists are concerned about the curtailment of Tibetan expression in Nepal.
"The community in Nepal needs space in which to peacefully express their anguish and their solidarity, particularly at a moment as significant as the March 10 anniversary," said Kate Saunders of the US-based International Campaign for Tibet.
"Tensions will only increase if this is not possible," she said.
In Taiwan on Sunday hundreds of slogan-chanting Tibetan activists and their Taiwanese sympathisers marched peacefully through the capital in protest at Chinese rule of Tibet.
Since 2009, 107 Tibetans have set themselves on fire to protest against China's rule and at least 90 have died.