"ISIL militants beheaded five young men in front of a crowd of people in central Mosul," Captain Qassim Juma, an intelligence officer in the Iraqi army’s Nineveh Operations Command, told Anadolu Agency.

Citing "information gleaned from sources inside the city via social media", Juma said the five men had been caught marking ISIL vehicles with a view to providing Iraqi forces -- backed by a U.S.-led air coalition -- with targets during an anticipated attack on the city.

In mid-2014, ISIL captured Mosul before overrunning large swathes of territory in northern and western Iraq. Recent months have seen the army -- backed by a 60-nation air coalition led by the U.S. -- retake much territory.

Nevertheless, the extremist group remains in control of several parts of the country, including Mosul, which officials in Baghdad have vowed to "liberate" by year’s end.