The United Nations' head for human rights has called upon Libyans to unite and resist the influence of the extremists in their country.

The security situation in Libya is currently in a vacuum following the overthrow of long-time dictator Muammar Gaddafi in 2011. Despite the election of a government in 2012, extremism in the country rose involving the same rebels that fought against Gaddafi's army in the civil war.

Some elements have now apparently affiliated themselves with the Islamic State, and are believed to have been behind the beheading of 21 Egyptian Christians on Sunday, earning the ire of Egypt and triggering retaliatory airstrikes from both the Egyptian and the Libyan air force.

According to the Human Rights Watch, at least six civilians were killed in the airstrikes in Libya's Derna.

In the wake of this latest tragedy involving ISIS, UN High Commissioner for Human Rights Zeid Ra'ad Al-Hussein urged Libyans to unite against the extremists.

"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," Zeid said in a statement. 

The term "tafkiri," refers to an event when a Muslim accuses another Muslim, or a person of another Abrahamic faith like Christianity or Judaism, of apostasy or insulting the Islamic religion. The term is attached to groups with hard-line Islamist ideologies like the Islamic State.

Zeid then reminded Libyans that the murder of the Egyptian Coptic Christians is against Islamic law.

"Murdering captives or hostages is prohibited under international law and Islamic law," he said.

The victims of the latest execution from ISIS had travelled to Derna in Libya to find employment but they were kidnapped in December and January.

Zeid revealed that this is not the first time that Egyptian Coptic Christians were targeted by extremist groups in Libya.

"UN human rights staff have documented several incidents involving abductions of Egyptian Copts in Libya," he said, referring to a recent United Nations report that revealed that Egyptian Copts are especially targeted by Libyan armed groups.