Washington, June 5 (Reuters): Despite highly publicised charges of US mistreatment of prisoners at Guantanamo, the head of the Amnesty International USA said today the group doesn’t “know for sure” that the military is running a “gulag”.

Executive director William Schulz said Amnesty, often cited worldwide for documenting human rights abuses, also did not know whether US defence secretary Donald Rumsfeld approved severe torture methods such as beatings and starvation.

Schulz recently dubbed Rumsfeld an “apparent high-level architect of torture” in asserting that he approved interrogation methods that violated international law.

“It would be fascinating to find out. I have no idea,” Schulz told Fox News Sunday.

A dispute has raged since Amnesty last month compared the prison for foreign terrorism suspects at the US naval base at Guantanamo Bay, Cuba, to the vast, brutal Soviet gulag system of forced labour camps in which millions of prisoners died.

A leading Democratic US senator today repeated his call for a full investigation and said the detention centre should be closed.

“The end result is, I think we should end up shutting it down, moving those prisoners. Those that we have reason to keep, keep. And those we don’t, let go,” Senator Joseph Biden of Delware told ABC’s This Week.

There have been a number of accusations of American mistreatment of the detainees and of the Quran, the Islamic holy book, at the base.

The US military on Friday released details about five cases top officials said were among only 10 reported over the course of more than 28,000 prisoner interrogations.

Schulz said, “We don’t know for sure what all is happening at Guantanamo and our whole point is that the United States ought to allow independent human rights organisations to investigate.”