The authorities in Libya have ordered protesters at a jail in Tripoli to return to their cells by the end of the day after violence erupted.
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A sit-in protest began at Abu Salim prison last week over trial delays.
Amnesty International say security forces fired live ammunition and tear gas at the prisoners, leaving one dead.
Hundreds were reportedly shot dead by guards during a protest over conditions in the same prison in 1996. The authorities are refusing to comment.
In recent years, Libya has been working to improve prison conditions.
Some 190 prisoners are said to be involved in the protest. Amnesty has called for an independent investigation into the alleged killing,
The prison is known to hold political prisoners, although the Libyan government has repeatedly denied such claims saying they are all Islamic fundamentalists.
Earlier this year Libya released 85 prisoners from the Muslim Brotherhood group.