The protest at the detention centre on the US naval base in eastern Cuba has swelled in recent weeks.

Military officials said that the hunger strikers are trying to gain public sympathy to pressure the United States to release them. But Ben Wizner, a lawyer with the American Civil Liberties Union, said: "The vast majority have never been charged with any crime and have been prevented from communicating directly with the outside world.

"So it may well be their attempt to ensure that the world is reminded of their unlawful detention."

Cmdr Robert Durand of the US navy said that 89 prisoners among the 460 suspected al-Qa'eda and Taliban supporters held at Guantanamo were participating in the hunger strike.

"All are being closely monitored by… medical staff and being counselled on the health effects of long-term hunger striking," he said.

But Clive Stafford Smith, a British-born lawyer working for several detained men, said he believed that the military was under-reporting the number of hunger strikers.