Islamic state militants executed a number of youths accused of joining an anti-ISIS faction by slicing them in half with chainsaws in the public square, a disturbing new report has revealed.

Iraqi News quoted a "well placed source" inside ISIS' stronghold Mosul that revealed the horrific execution: "The death sentence pronounced by ISIS sharia court stated that the men should be tied to an iron pole in the center of Tal Afar Square in Mosul and then sliced into two with an electric chainsaw," the anonymous source said.

Since overtaking the main city in northern Iraq in 2014, the militants have executed a number of citizens in various grotesque ways, often forcing the public to watch.

Earlier this year, Iraqi News reported ISIS killed six men accused of being "spies" by boiling them to death in vats of tar. The executions were carried out at an ISIS command center in al-Shora in Iraq, "with the aim of inciting fear among the citizens".

"ISIS executed six persons in Mosul for collaborating with Nineveh Operations Command," read the report. "The six persons were placed inside tanks containing boiling tar and the execution was carried out in one of Isis headquarters at al-Shora. The execution took place... with an aim of inciting fear among the citizens."

Media activist Abdullah al-Malla told the Kurdish news site ARA News that hundreds of citizens were present and forced to listen as an IS official read the charges against the men before the execution was carried out.

"Those mercenaries have cooperated with the crusader coalition and the Peshmerga in order to destroy the Caliphate territory and kill innocent Muslims in the name of freedom and democracy," the IS official was quoted as saying. "The Caliphate [Islamic State] will show no mercy to such traitors."

The Daily Mail reports that ISIS fanatics have meanwhile threatened to carry out new lone wolf attacks on the West after their propaganda chief,  Abu Mohamed al-Adnani,  was killed in an air strike in Aleppo, Syria earlier this week.

According to the respected Site Intelligence Group, which monitors jihadist activity, the threats were made on a pro-ISIS account on the encrypted Telegram messaging service, warning: "We will exterminate you".

In April, U.S. President Barack Obama said that he expected Mosul to be retaken from ISIS by the end of 2016, and on Tuesday a top U.S. general said they were on track to meet the target.