The United Nations special rapporteur on torture, Manfred Novak, has accused the United States of using cruel methods to force feed hunger strikers at Guantanamo Bay.
He was speaking after the US military revealed that there were now at least 80 detainees refusing meals, the number taking part in the five-month-old protest having more than doubled since Sunday.
Mr Novak said visiting lawyers had made plausible and well-substantiated allegations of cruelty.
Lawyers for some of the prisoners say they are protesting against their conditions and lack of legal rights.
Officials at Guantanamo Bay say doctors are force-feeding 32 of the hunger strikers with plastic tubes.