A video purportedly released by the Islamic State warns Christians, whom it calls "followers of the cross," all over the world including the United States—which it calls "the protector of the cross"—will not have peace and instead face shame "in life and in eternity" unless they convert to Islam and follow its customs and beliefs.

The warning was included in a recently released video which shows ISIS militants executing three Assyrians late last month. The video footage also shows members of the jihadist group threatening to kill some 200 other Christians and Catholics in Syria unless a ransom of $50,000 for each of them is paid for their release, according to Christian News.

The video footage shows three men in desert uniform executing three men dressed in orange jumpers after they uttered their names and the town they came from.

The men identified themselves as Ashur Abraham of Tel Tamar village, Basam Essa Michael of Tel Shamiram village and Dr. Abdulmasih Enwiya of Jazira village.

After the shooting, the video shows another three men being prepared for execution. But in an apparently scripted scene, one of them points to the bodies on the ground and says, "Our fate is the same as these if you do not take proper procedure for our release."

Citing Arabic-language news media, Christian News said the videotaped execution could have taken place during the Muslim holiday of "Festival of the Sacrifice" last Sept. 23.

The six men on the video tape were among the 250 Assyrians captured by ISIS in February when they attacked Assyrian villages near the Khabur River Valley in Hassakah Province, the report said.

ISIS has reportedly released eight hostages and demanded more than $10 million for all of those abducted. If ransom is not paid, they will be executed.

The video came days after the ISIS released another video about the "submission tax" imposed on Christians and other religious groups in the town of Al-Qaryatayn, which they seized last Aug. 5.

Wealthy Christians were required to pay an annual jizya (submission tax) of four gold dinars; middle-class Christians, two gold dinars, and the poor, one dinar.

In September, the ISIS also issued photographs of Christians and others gathered in an auditorium signing the Dhimma document, which delineates their second-class status. Those who stayed in Al-Qaryatayn agreed to several stiff conditions, including abiding by the ISIS dress code and commerce guidelines and not engaging in business activity involving pigs or alcohol with Muslims or in Muslim markets, among others.

"...As for the situation of the Nazarenes [Christians], a group of them converted to Islam, while others made peace and signed an Al-Zema [Dhimma] contract and preferred to live and enjoy the peace and safety under the ruling of Islam in the Islamic State," said a voice on the video , believed to be an ISIS leader.

If contract is broken, he warned that they will "face the same conditions as the people of war."