Havana ? American activists camping out at a Cuban military checkpoint outside the U.S. naval base at Guantanamo Bay started their first day of a water-only fast Monday to protest the treatment of suspected terrorists detained at the base.

Members of the largely Christian group Witness Against Torture are demanding access to the prisoner camp to meet with inmates. The activists arrived late Sunday at the checkpoint, which is about five miles from the U.S. base.

U.S. officials insist the hundreds of prisoners held at Guantanamo are treated humanely at the remote base on Cuba’s eastern tip. The government says they are enemy combatants, not prisoners of war, and are not entitled to the same rights afforded under the Geneva Conventions.