An Egyptian photojournalist who has spent over 600 days locked up without any charges describes his prison as a "cemetery" and his indefinite detention as "psychologically unbearable" in a letter published by a rights group.

Mahmoud Abou-Zeid, known by his nickname Shawkan, was arrested in August 2013 while taking photographs of the government's violent dispersal of a sit-in by supporters of ousted Islamist President Mohammed Morsi. Over 600 people were killed in the dispersal.

Since then, the 27-year-old photojournalist has been held without charges, interrogated on suspicion of taking part in a violent Islamist protest. Abou-Zeid calls the accusations "fabricated," and said he was taking pictures of what felt like "a war."

Abou-Zeid's brother, Mohammed, said Tuesday the letter was sent last weekend. Amnesty International later published it.