The Burma Media Association, a grouping of exiled journalists, has renewed its call for the release from prison of pro-democracy activist and journalist U Win Tin.

The 77-year-old journalist has served 18 years of a 20-year prison sentence on various charges related to his activism.

In March, United Nations human rights expert Paulo Sergio Pinheiro said U Win Tin is one of more than 1,000 people currently in Burmese prisons for exercising their rights to free speech and free assembly.

Pinheiro noted that U Win Tin has received three additional prison terms since his original incarceration in 1989. The last came for a letter he wrote to an international organization about the ill treatment of political prisoners.

The media group says U Win Tin has repeatedly refused to sign a government document requiring him to give up political activities in exchange for his freedom.

The Southeast Asian Press Alliance issued a similar appeal Monday on U Win Tin's behalf. In a statement, the group said U Win Tin's principal crime, in the eyes of the state, was his work as a key advisor to pro-democracy activist and Nobel laureate Aung San Suu Kyi.

Aung San Suu Kyi, the daughter of independence hero Aung San, has been under some form of detention for most of the past 18 years.