Paris (dpa) - The World Association of Newspapers (WAN) on Thursday intensified its campaign to obtain the release of jailed Vietnamese editor and academic Doan Viet Hoat, who is to receive the global newspaper group's annual press freedom prize early next month.

In letters to Vietnam's leaders, WAN President Jayme Sirotsky urged Hanoi to release Professor Doan, who is to receive the Golden Pen of Freedom before an audience of over 1,000 editors and publishers at the World Newspaper Congress in Kobe, Japan, on June 1.

A similar letter, and information about Doan's case, was posted on the WAN website (www.fiej.org), along with an appeal to the world's press and other interested parties to send the letter to Vietnam's leaders and join the campaign for Doan's release.

Doan, editor and publisher of the pro-democracy newsletter Dien Dan To Do (Freedom Forum), was sentenced in March 1993 to 20 years of hard labour for his work with the newsletter. He is serving his sentence, commuted to 15 years on appeal, in Thanh Cam prison.

Doan is reportedly in poor health and suffers from kidney stones. His three brothers tried to visit him on February 5, but were not allowed to see him. The reason given by prison officials was that Doan had made ``very poor progress'' in his ``re-education''.

No independent source or family member has seen him since 1996.

``I respectfully remind you that Professor Doan has been imprisoned simply for exercising his right to freedom of expression,'' Sirotsky said in his letters to President Tran Duc Luong, Prime Minister Phan Van Khai, and Communist Party Secretary General Le Kha Phieu.

WAN awarded its 1998 Golden Pen of Freedom to Professor Doan in recognition of his courage in the struggle for freedom of expression and freedom of the press in Vietnam. Presentation of the award is to be made at 51st World Newspaper Congress and 5th World Editors Forum, the annual meetings of the world's newspaper industry.

The events are being organised by the World Association of Newspapers - the global association of the newspaper industry, representing 15,000 newspapers world-wide - and the Japan Newspaper Publishers and Editors Association.

The Golden Pen of Freedom has been awarded annually since 1961 to recognise the outstanding action, in writing or deed, of an individual, group or institution in the cause of press freedom.