The United Nations human rights chief on Tuesday condemned the mass beheadings of Egyptian Christians in Libya and urged Libyans to fight the extremists in their country.

The United Nations human rights chief on Tuesday condemned the mass beheadings of Egyptian Christians in Libya and urged Libyans to fight the extremists in their country.

"The brutal murder of these men, and the ghastly attempt to justify and glorify it in a video, should be roundly condemned by everyone, in particular by the people of Libya who should resist the urgings of Takfiri groups," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said in a statement.

ISIL militants in Libya posted a video on Sunday showing the decapitation of 21 Coptic Christians who were in the country seeking work.

"Murdering captives or hostages is prohibited under international law and Islamic law," he said, denouncing what he called a "vile crime targeting people on the basis of their religion."

UN human rights staff said Egyptian Coptic Christians have been abducted before in Libya.

In one case in December, "the bodies of three members of a Coptic Christian family were found in Sirte," the high commissioner's office said.

"Churches and other religious sites have also been attacked in Libya over the past three years," it added.

Zeid meanwhile urged Egypt to avoid civilian casualties, after it launched air strikes on ISIL group targets in Libya in retaliation for the beheadings.

"The Egyptian air force must ensure full respect of the principles of distinction between civilians and fighters, and civilians objects and military objectives," Zeid said.