A video released Sunday showed the beheading of 21 Egyptian Coptic Christians in Libya by ISIS militants.

The video, being widely circulated on the Twitter accounts of ISIS supporters, is titled "A Message Signed With Blood to the Nation of the Cross."

The location is said to be near Tripoli, Libya, making it the first video in which ISIS apparently carried out an execution outside of the territory the militant group seized in Iraq and Syria.

Like previous ISIS beheading videos, the footage is highly edited with slick production values. It opens with the men in orange jumpsuits being led along a beach purportedly on the Mediterranean by men in black with masks.

"Safety for you crusaders is something you can only wish for," the man says.

In a message to the "crusaders," a masked man holding a knife says the group is "chopping off the heads of those that have been carrying the cross illusion."

The men's heads are then shown removed from their bodies, while blood mixes with the waves.

Official: Kerry “offered his condolences on behalf of the American people and strongly condemned the despicable act…”

Official: Kerry “offered his condolences on behalf of the American people and strongly condemned the despicable act…”

Secretary of State John Kerry offered condolences Sunday night as Egyptian leaders considered their response to the killings.

A statement from the White House condemned the "heinous act" and called for support of United Nations' efforts to resolve conflict in Libya:

Describing the slain men as "martyrs of the righteous," the church spokesperson vowed not to rest until the "wicked perpetrators" are brought to justice.

The names of the slain Christians were released by the Coptic Church's Bishop Anba Ermia on Twitter , and translated into English by D.C.-based lawyer Mai El-Sadany.

Names of executed Egyptians. May they rest in peace.

18. Gaber Munir Adly 19. Esam Badir Samir 20. Malak Farag Abram 21. Sameh Salah Faruq Names of executed Egyptians. May they rest in peace.

PM: The murder of 21 Egyptian Coptic Christians is a cruel & barbaric act. We will not waver in our fight against terrorists & extremism.

PM: The murder of 21 Egyptian Coptic Christians is a cruel & barbaric act. We will not waver in our fight against terrorists & extremism.

British Prime Minister David Cameron condemned the video, describing it on Twitter as a "cruel and barbaric act."

The new video follows the horrific footage released by ISIS earlier this month showing the death by fire of captured Jordanian pilot Muath al-Kaseasbeh.

His brutal murder unleashed a wave of anger in Jordan, with the government promptly executing three convicted terrorists who had long been on death row.

Last week, the U.S. government confirmed the death of Kayla Jean Mueller, an American woman who died after more than a year in ISIS captivity.