The Islamic State jihadist group has released a video purportedly showing the executions of some 30 Ethiopian Christians captured in Libya.

The 29-minute video purports to show militants holding two groups of captives, described in text on the screen as "followers of the cross from the enemy Ethiopian Church".

A masked fighter brandishing a pistol makes a statement threatening Christians if they do not convert to Islam.

The video then switches between footage of one group of about 12 men being beheaded by masked militants on a beach and another group of at least 16 being shot in the head in a desert area.

It was not immediately clear who the captives were or exactly how many were killed.

Before the killings, the video shows purported footage of Christians in Syria explaining how they had been given the choice of either converting to Islam or paying a special tax, and had decided to pay.

The video bore the logo of Islamic State's (IS) media arm and was similar to footage released in the past, including of a group of 21 Coptic Christians, mainly Egyptians, beheaded on a Libyan beach in February.

Several Libyan jihadist groups have pledged allegiance to IS, the extremist organisation that seized control of large parts of Syria and Iraq last year and declared an Islamic "caliphate".

IS has carried out widespread violent atrocities and won the support of jihadist groups across the region, including in chaos-hit Libya.

Attacks raise fears for Christians in Middle East

UN-backed efforts to form a national unity government have made little progress and officials have warned that Libya - awash with weapons after former leader Moamar Gaddafi's overthrow - threatens to become a haven for jihadists on Europe's doorstep.

IS has persecuted minorities including Christians and its executions of the Egyptian Copts prompted retaliatory air strikes from Cairo.

Egypt called for an international intervention against the jihadists in Libya but Western diplomats expressed reservations, saying a political deal must be the priority.

A US-led coalition of Western and Arab nations is carrying out an air war against IS in Syria and in Iraq, where pro-government forces have managed in recent months to retake some territory seized by the group.

The group's attacks have raised fears for Christians across the Middle East and been condemned by religious leaders.

The head of the Church of England, Archbishop of Canterbury Justin Welby, was in Egypt on Sunday to offer his condolences over the beheadings of the Copts in Libya.

He was to meet president Abdel Fattah al-Sisi, Sheikh Ahmed al-Tayeb, grand imam of Al-Azhar, the highest Sunni Muslim authority, and Coptic Pope Tawadros II.

Almost two-thirds of Ethiopians are Christians, the majority of those Orthodox Copts - who say they have been in the Horn of Africa nation since the first century AD - as well as large numbers of protestants.

Many Ethiopians leave their country - Africa's second largest in terms of population with more than 90 million people - seeking work elsewhere.

Many travel to Libya and other north African nations for jobs, as well as to use it as a stepping stone before risking the dangerous sea crossing to Europe.

AFP