(AFP) The family and friends of Swiss environmental activist Bruno Manser, who disappeared on Borneo island 15 months ago, believe he may have perished, a Swiss official said today.

John Kunzli, secretary of the Bruno Manser Fund in Basel, said a second search expedition to Sarawak state, led by Manser's brother earlier this month, failed to find any trace of him.

"It is very difficult for us, his friends and families, his office and companions in the struggle, to believe he is still alive," Kunzli told AFP in a telephone interview.

Month-long search

He said Manser, a staunch defender of the nomadic Penan tribe and the rainforest in Sarawak, returned to the state on May 23 last year and had not been heard of since sending a letter to his Swiss girlfriend dated May 25.