Islamic State in Libya has claimed responsibility for abducting Christians there in a statement received by the SITE intelligence group, which monitors the electronic communications of jihadis.

The statement read: "Urgent. Soldiers of the Islamic State captured 21 Christian crusaders."

Photoshopped pictures of several men were posted alongside the statement. A farmer from Minya in Upper Egypt, Bisheer Estefanos, said he recognised the faces of his brothers, Bishoy and Samuel. "All we can do is pray to God for help," he said. "Their mother is tired of crying."

Reports earlier this month said that 20 Coptic Christians in two groups, at least some of them from Egypt, had been kidnapped in the Sirte province over several days.

It was later reported that 13 of the men had been released, but this information was never confirmed.

The 13 were abducted when gunmen stormed a residence for expatriates in Sirte, according to Magdy Malik, a Christian activist in Egypt

Gunmen went room to room and asked for identification papers to separate Muslim workers from Christians, witness Hanna Aziz told The Associated Press.

"They were 15 armed and masked men who came in four vehicles," he said. "They had a list of full names of Christians in the building. While checking IDs, Muslims were left aside while Christians were grabbed. I heard my friends screaming, but they were quickly shushed at gunpoint. After that, we heard nothing. I am still in my room waiting for them to take me. I want to die with them." He said he escaped capture because he didn't open his door.

Libya has descended into chaos after the fall of the Gaddafi regime in 2011 following a civil war in which Western air strikes were used to back his opponents. A weak central government has been unable to impose order on the various tribal and other factions which emerged after the war. Sectarian killings are commonplace and rival militias are battling for control of resources.

As many as 10,000 Egyptians work in the country, mainly in the construction sector. They are frequently targeted by extremists. In December a 13-year-old girl was abducted by armed men and killed in a suspected religiously motivated attack, while in February last year the bodies of seven Egyptian Christians who had been shot were found near Libya's second city, Benghazi. The previous year, militiamen abducted and tortured several dozen others.