No prisoner faces any immediate health threat from the strike, though two have been admitted to the prison medical clinic because of dehydration, said Navy Capt. Robert Durand, a spokesman for the detention center at the U.S. base in Cuba.

In recent weeks, as lawyers returned from Guantanamo with accounts of clients weak from hunger and an angry standoff with guards, the military had said no more than a handful of prisoners met the definition of being on hunger strike, which includes missing nine consecutive meals.

That figure rose to 14 on Friday, and then grew by seven over the weekend. It has become the largest and most sustained protest at Guantanamo in several years, but Durand insisted there is no evidence to support reports of a strike involving most of the 166 men held there.