Updated

The family of an American prisoner of war captured four years ago in Afghanistan says it has received a letter it believes was written by him.

Sgt. Bowe Bergdahl of Hailey, Idaho, disappeared from his base in Afghanistan on June 30, 2009, and is believed held in Pakistan.

His mother and father in Idaho issued a statement on Thursday saying they've received a letter they are confident was written by their son.

In the statement, Bob and Jani Bergdahl say the letter, delivered through the International Committee of the Red Cross, gives them hope that their son is doing as well as can be expected, under the circumstances.

They thanked the Red Cross for its help and support -- and renewed their plea for his captors to release him.