WASHINGTON, Sept 13 (AFP) - US-based Tibetan activists plan vigils in 13 American cities next week marking one year since a Tibetan scholar studying in the United States vanished during a trip to his Himalayan homeland.

"We want to achieve the release of Ngawang Choephel," said Mary Beth Markey, director of government relations at the International Campaign for Tibet (ICT). "We want to encourage the Chinese government to give him a fair and public trial or to set him free."

To step up pressure for his release, ICT and other Tibetan groups have planned events in 13 US cities next week marking the anniversary of his disappearance.

Choephel, 30, who fled Tibet with his parents as a young child, grew up in India and came to Middlebury College in Vermont as a Fulbright scholar in ethnomusicology in 1993.

During a visit to his native country in September 1995, Choepel vanished.

A fellow Tibetan reported seeing him soon afterward in Nyari prison in Shigatse, west of the Tibetan capital Lhasa, ICT said.

The reasons for Choepel's disappearance are unclear, Markey said, adding that he was not involved in political activities that the Chinese authorities who have governed Tibet since the 1950s find objectionable.