A group of Islamic extremists - supposedly with ties to Islamic State (Isis) - have threatened Christians in Israel and the Palestinian territories that they will be slaughtered unless they leave by the end of Ramadan.

The Muslim holy month ends with the Eid al-Fitr festival on 17 July.

The group, calling itself Islamic State, Emirate of Bayt al-Maqdis, or the Holy City, meaning Jerusalem, reportedly began distributing the message via leaflets in Beit Hanina, in north Jerusalem, according to the Jerusalem Post.

The leaflets said: "Those who work with the Zionists also encourage Muslims to leave their religion and become more secular and open, and they spread evil.

"They take these Muslims away from us.... We know where they are, but we need help to find them all – all those Christian collaborators."

Despite bearing Isis's logo, some Israeli Arabs - Muslims and Christians - questioned the leaflets' veracity.

The leaflet added: "Isis soldiers will work to kill these people so this country is clean of them and... will clean this country and the Muslim Quarter from these Christians during this holy Ramadan."

It added that the group's operatives will begin their search in Beit Hanina and Shuafat, another northern Jerusalem suburb, as well as the Muslim Quarter of the Old City and the Church of the Holy Sepulchre.

"Because the Christians violated the Pact of Omar [made when Muslims conquered Jerusalem], we will do this," the note concluded. "So we tell our Christians and the non-believers: 'Go away now or you will be killed when the Eid is near.' And you will be slaughtered like the sheep. One month is enough for them to go away."

An Israeli with many Christian Arab friends told the Jerusalem Post: "They're fearful for their lives and don't want to go to the police because they feel that the police won't be responsive.

"What's most problematic is that in this case individuals aren't being targeted but an entire group, which is pretty darn serious," he continued.

"If leaflets with swastikas and similar threats were sent to Jewish neighbourhoods, people would be outraged. I hope and pray it amounts to nothing at all."