An Islamist armed group carried out a videotaped execution of the Egyptian man in a stadium in Derna in the east, in what Amnesty said yesterday highlighted Libya's descent into lawlessness.
The rights group said the killing was carried out on August 19, apparently by an extremist militant group, the Shura Council of Islamic Youth, in front of a crowd seated in the stadium.
"Egypt utterly condemns the murder of its citizen, who had no recourse to a fair trial," foreign ministry spokesman Badr Abdelatti said in a statement.
He is forced to kneel and a statement is read out accusing him of killing a Libyan, Amnesty said.
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A gun is then passed to an unmasked man in plain clothes, believed to be the brother of the dead Libyan, who then shoots Mohamed from behind.
Abdelatti today urged "all regional and international parties to support the Libyan authorities in confronting extremists, help rebuild Libyan state institutions and re-establish security, law and order and justice".
Since the fall of long-time dictator Muammer Gaddafi in a NATO-backed 2011 uprising, Libya's interim authorities have failed to establish order and security in a country prone to anarchy and deadly violence.