Updated

Libyan authorities have recovered the bodies of 21 Coptic Christian workers, mostly Egyptians, beheaded in 2015 by the Islamic State group in the coastal city of Sirte.

Saturday's statement by the media office of anti-Islamic State organization al-Bonyan al-Marsous, says an arrested IS militant, who witnessed the attack, provided details on the incident and the militants involved.

The beheaded bodies in orange uniforms were found with their hands cuffed to the backs, the group says. They included 20 Egyptians and one African.

The killings were documented in a grisly video released online by the extremists that shocked Egypt and led it to launch punitive airstrikes.

Libya has descended into chaos since a popular 2011 uprising that toppled and later killed longtime dictator Moammar Gadhafi.