Islamic State (Isis) has killed eight of its Dutch fighters for "desertion and mutiny" in Raqqa city in Syria, one of the members of citizen journalist group called Raqqa is Being Slaughtered Silently (RBSS) said on Twitter. Abu Mohammad said the killings come after a month of tensions between 75 Isis (IS) Dutch fighters, some of whom are of Moroccan origin, and the terror group's intelligence unit based in Iraq.

"Daesh [Isis] executed eight Dutch fighters on Friday in Maadan, Raqqa province, after accusing them of attempting desertion and mutiny," Mohammad said.

RBSS said IS leaders had sent a delegate to the Dutch fighters in order to settle any differences that might have cropped up between them, but instead the fighters killed him. With the murder of the delegate, IS fighters from Iraq arrested and imprisoned the Dutch fighters in Tabaqa and Maadan in Syria, RBSS said. The Dutch fighters were later executed, RBSS added.

RBSS has been monitoring IS brutality in its stronghold in northern Syria since April 2014.

Mohammad also said Isis fighters based in Iraq arrested three other Dutch fighters, accused of trying to flee the terror group. One arrested fighter was beaten to death during interrogation, he said.

The Syrian Observatory for Human Rights (SOHR), which has been monitoring the conflict, could not verify the killings. However, it said three IS fighters of North African origin from Europe were killed in Wilayet al-Furat, an area spanning the border between Syria and Iraq.

Dutch secret services have said around 200 people from the Netherlands, including 50 women, have joined IS in Syria and Iraq, the Guardian reported.

In December 2014, IS killed 100 of its foreign fighters, who were accused of trying to flee Raqqa. In October of the same year, IS imprisoned 12 of its European fighters in Syria, who wanted to return to their homes because they were fighting rebel groups instead of President Bashar Assad's forces.

"The situation is not good. We aren't able to speak the truth, and we are forced to do useless things," one foreign fighter was quoted as saying by the Financial Times.