Thirteen teenagers in Mosul, Iraq reportedly met a violent death at the hands of an ISIS firing squad last week.

Their offense? They enjoyed a game of football on the television.

The Daily Mail reports that the Islamic State had caught the 13 teenagers while they were watching a telecast of a football game between Iraq and Jordan for the Asian Cup on January 12.

The executions are believed to have taken place in the Al-Yarmouk district in Mosul, and were reported by the activist group Raqqa is Being Slaughtered Silently through its website. The group works to document the human rights abuses committed by ISIS in its home city.

According to the group, ISIS announced the 13 teenagers' offence through a loudspeaker prior to their execution.

"The bodies remained lying in the open and their parents were unable to withdraw them for fear of murder by terrorist organisation," the group described on its website.

The execution was reported together with other murders committed by ISIS last week in Iraq. The Daily Mail also described two men being hurled to death from a tower while blindfolded in front of a large crowd. These men were accused of homosexuality and sentenced by an ad hoc court, the New York Times reported.

The same New York Times article said two ISIS members had been executed in Mosul for banditry. They were crucified and shot.

News.com.au reports that ISIS subjected 17 young men to crucifixion in an unnamed village in Iraq and also shot them, while a woman was also accused of adultery and sentenced to death by stoning in another unspecified location in Iraq.

The United Nations described the killings as "another terrible example of the kind of monstrous disregard for human life that characterises ISIL's reign of terror over areas of Iraq that are under the group's control," the New York Times said.