The Islamic State group (IS) has executed 700 people from a Syrian tribe it has been battling in eastern Syria over the past two weeks, the majority of whom were civilians, a Syrian monitoring group said Saturday.

The British-based Syrian Observatory for Human Rights, which has consistently tracked violence on both sides of the three-year-old Syrian civil war have said that around 700 members of the al-Sheitaat tribe, from the Deir al-Zor province, have been executed and that many of them were beheaded by IS jihadists.

"Those who were executed are all al-Sheitaat," Observatory director Rami Abdelrahman told Reuters by telephone from Britain. "Some were arrested, judged and killed."

The conflict sucked in the al-Sheitaat tribe, who are about 70,000 in number, after the Islamic State captured two oil fields in July.

Sheikh Rafaa Aakla al-Raju, the head of the al-Sheitaat tribe, told other tribes to join the fight in a video message posted on YouTube on Sunday.

"We appeal to the other tribes to stand by us because it will be their turn next ... If (Islamic State) are done with us the other tribes will be targeted after al-Sheitaat. They are the next target," he said.

The latest IS slaughter in their battle to create a medieval style caliphate across northern Iraq and Syria, come after 80 members of the Yazidi minority were massacred by IS militants in Iraq on Friday.

A senior Kurdish official told Reuters that he believed the Yazidi men had been killed because they refused to convert to Islam.

“We believe it because of their creed: convert or be killed.”

According to BasNews, a Kurdish website, the village of Kojo came under attack by IS radicals. The entire male population of the village was slaughtered and all the women and children were abducted.

In the Syrian province of Aleppo several towns and villages were seized by IS radicals from other Islamic groups earlier in the week.