Several hundred Tamils started an open-ended demonstration in Bern on Tuesday to draw attention to what they describe as "genocide" in Sri Lanka.
The coordinator of Tamil organisations in Switzerland, Krishna Ambalavanar, has written an open letter to the Swiss foreign minister Micheline Calmy-Rey, warning that he will fast to the death unless their demands are met.
The demonstrators gathered outside the offices of the foreign ministry to back their demands that Switzerland should intervene "to stop the genocide". They want medical and other humanitarian supplies to be sent to people trapped by fighting in the northern Vanni region.
They also want a special session of the United Nations Security Council to discuss the situation and to call on the Sri Lankan government to allow the Tamils to vote on partition.
Foreign ministry officials received a delegation in the late afternoon to hear their demands. The officials repeated Switzerland's policies over the issue.
Tamil Tiger rebels in Sri Lanka have been fighting for a separate state in the north and east of the island since the 1970s. Earlier this year government forces launched a widescale offensive against the Tigers, in the hope of bringing the conflict to an end.
Tens of thousands of civilians have been trapped by the fighting or forced to flee their homes.
Both the government forces and the Tamil Tigers have been regularly accused of gross human rights abuses.
Sri Lankan Tamils are one of the biggest migrant groups in Switzerland.
swissinfo with agencies