Archbishop of Canterbury Justin Welby described Islamic State (IS) as "deeply evil", after news broke on Sunday that 30 Christians had been killed by the jihadist group in Libya.

Welby travelled to Egypt on Saturday to meet with religious and political leaders in the country, and express his condolences for the murder of 21 Egyptian Christians in Libya in February. While he was there IS released another of its propaganda videos, purporting to show around 15 Ethiopians being beheaded, and another group of the same size being fatally shot in the head.

In the video the victims are referred to as "worshippers of the cross belonging to the hostile Ethiopian church". Country authorities have said that they were likely to have been migrants travelling through Libya in the hope of reaching Europe.

"I believe Islamic State is deeply evil – even to its own supporters if they stray one inch off what is seen as the right road," Welby said in an interview with the BBC this weekend. He has previously backed military action against the group, repeatedly condemning the gross violations of the fundamental rights and freedoms of minority communities in Iraq and Syria.

In an article for Prospect magazine last October, Welby praised the "strong and brave tradition of absolute pacifism" favoured by some Christians, but said that religious leaders in the Middle East have asked for armed assistance.

"They seek temporary support while their own governments get their act together. They do not want the Middle East emptied of its Christian populations, essential to its culture, critical in many areas of life and there since before the time of St Paul," Welby explained.

"There is a need to struggle for the values that our own centuries of insane conflict have taught us to treasure. Sometimes this may temporarily include armed force on an international scale."

Speaking to the BBC, Welby said that to turn our backs on those struggling under persecution is "totally unacceptable", but added that finding a solution will not be simple. "To say...'you will leave that area and come to our place' – we all know that that is, again, an invitation to ethnic cleansing on a grand scale."

Following the Archbishop's comments, the General Bishop of the Coptic Orthodox Church in the UK, Bishop Angaelos, released a statement condemning the latest IS murders.

"The confirmation of the murder of Ethiopian Christians by Daesh (IS) in Libya has been received with deep sadness. These executions that unnecessarily and unjustifiably claim the lives of innocent people, wholly undeserving of this brutality, have unfortunately become far too familiar. Once again we see innocent Christians murdered purely for refusing to renounce their Faith," he said.

"The Christians of Egypt and Ethiopia have had a shared heritage for centuries. Being predominantly Orthodox Christian communities with a mutual understanding of life and witness, and a common origin in the Coptic Orthodox Church, they now also share an even greater connection through the blood of these contemporary martyrs."

Bishop Angaelos said he was thankful for the solidarity of communities from all over the globe, and that "in the midst of this pain...the ghastly nature of these crimes is bringing a greater rejection of them, and of any ideology that sanctions, justifies or glorifies brutality and murder."

He urged those of religious belief and none to speak out against the violence, but also for Christians in particular to pray for the victims, their families, and those who are committing the atrocities.

"As Christians, we remain committed to our initial instinct following the murder of our 21 Coptic brothers in Libya, that it is not only for our own good, but indeed our duty to ourselves, the world, and even those who see themselves as our enemies, to forgive and pray for the perpetrators of this and similar crimes," he said.

"We pray for these men and women, self-confessed religious people, that they may be reminded of the sacred and precious nature of every life created by God."

He concluded: "Having seen the courageous response of the families of the Coptic martyrs in Libya, we pray similar strength, courage and peace for all those suffering as a result of this brutal act, reassured that their loved ones will never be forgotten, having died as true martyrs and paying the ultimate price, hearing the joyful promise 'Well done, good and faithful servant...enter into the joy of your Lord.'"