Bishop Angaelos has also expressed "deep sadness" over their deaths, calling them true martyrs.
He was speaking after Islamic State released a video on Sunday appearing to show members of the extremist group kill 30 Ethiopian Christians in the North African state.
15 of them appeared to be beheaded on a beach, whilst the other 15 were shot in the head in a desert.
It's the second time Islamic State has posted a video showing them kill Christians in Libya. In February, they released a video showing them kill 21 Egyptian Coptic Christians who were migrant workers in Libya.
Bishop Angaelos told Premier: "The confirmation of the murder of Ethiopian Christians by Daesh (IS) in Libya has been received with deep sadness.
"Once again we see innocent Christians murdered purely for refusing to renounce their Faith.
"I am thankful, in the midst of this pain, that 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.
"... 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.
"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.
"We pray repose for the souls of these innocent men, a change of heart for those who took their lives, but above all we pray comfort and strength for their families and communities, and the many around the world who may not have known them, yet are left to mourn such a tragic and unnecessary loss of precious life."
The Ethiopian Information Minister Redwan Hussein has said their government is trying to establish the identity of the 30 murdered Christians, and has said: "we strongly condemn such atrocities, whether they are Ethiopian or not."
Islamic State's purported killing of 30 Ethiopian Christians is part of its campaign to establish what it calls an Islamic caliphate, or kingdom, in the Middle East.
The extremist group has killed hundreds of Christians under a convert or die ultimatum, and has forced tens of thousands to flee their homes, as well as Muslims and other religious minorities such as the Yazidis.
Listen to Hannah Tooley speak with Bishop Angaelos here: