A UN official who declined to tour Guantanamo Bay Detention Center after he was told he would not have unlimited access to detainees, accused the US of force-feeding detainees at the prison.
Manfred Nowak’s comments came after it emerged that the number of detainees refusing food at the prison camp had more than doubled since 25 December.
Some 84 inmates are now refusing food, according to the US military.
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But a Pentagon official said there was no evidence that they had been treated in an inappropriate way.
Mr Nowak has not been to Guantanamo, and turned down an invitation to the camp because the US refused to give him unrestricted access to the detainees.
He told the BBC that he had received reports that some hunger strikers had had thick pipes inserted through the nose and forced down into the stomach.
This was allegedly done roughly, sometimes by prison guards rather than doctors. As a result, some prisoners had reported bleeding and vomiting he said.