Libyan authorities have arrested a suspected Islamic State militant they believe was involved in the beheading of 21 Egyptian Coptic Christians in Libya.
Chief prosecutor Al-Sadiq al-Sour told reporters the killings took place in 2015 behind a seaside hotel in the coastal city of Sirte.
He said authorities have also identified the site where the bodies were buried.
The killings, documented in a grisly video released online by the extremists, shocked Egypt and led it to launch punitive airstrikes.
Mr Al-Sour said IS militants have been using Sudan, the country's southern neighbour, to get into Libya.
Hundreds of IS militants are believed to have fled Sirte into the Libyan interior after their defeat last year by militias loyal to a UN-backed government in Tripoli, the capital.