A video released by the Islamic State group Sunday purports to show two separate groups of captives being killed, one by beheadings and the other by gunfire, the Associated Press reported. The authenticity of the video has not yet been verified.

The footage of the two apparently doomed groups -- believed to consist of Ethiopian Christians captured by the Islamist militant organization formerly known as either ISIL or ISIS -- comes after a speech by a masked fighter holding a pistol while delivering a long statement about Christians’ duty to convert to Islam or pay a special tax described in the Quran. The 29-minute video bears the logo of the Islamic State group’s media arm Al-Furqan, AP said.

The video is similar to previous releases by the extremist group, such as the one in February that depicted militants in Libya beheading 21 Egyptian Christian hostages on a beach.

ISIS beheading video In this scene from the Islamic State's latest purported beheading video, captives in black jumpsuits are shot by men whose faces are covered. The men killed are said to be Egyptian Christians. Photo: YNet

In the latest video, supposed Islamic State operatives march one group of captives to a beach area and the other group of hostages to a desert area. The first group is dressed in orange jumpsuits, and the second group in black outfits. A narrator says the first group was "adherent of the Ethiopian church," with the killings taking place in the Fezzan region Libya. The slayings of the second group purportedly took place in the Barqa region of the same country. A total of 28 people were killed in the video, according to the Jerusalem Post.

The Islamic State group has lately been advancing in Iraq, where AP reported its members captured three villages near the city of Ramadi in western Anbar province while engaged in heavy clashes with Iraqi troops. Saturday, militants with the group’s Afghanistan branch claimed responsibility for twin blasts in Jalalabad that killed at least 33 people. The claim remains unverified, but, assuming it is true, the bombings would constitute the first such attacks carried out by the Islamic State group in Afghanistan.