Iraq ISIS insurgents tweeted a photo of a police officer who they beheaded in the officer’s own home and accompanied the tweet with a depraved joke about using the murdered policeman’s severed head as a soccer ball — even including the hashtag #WorldCup in the text of the Twitter message.

Though the Twitter account that sent out the appalling message and photo has since been deleted, for at least a while innocent soccer fans could have come across the nightmarish image while simply searching for messages about the World Cup international soccer tournament currently underway in Brazil.

The radical insurgent group Islamic State in Iraq and Syria, tweeted the grisly image with a line that they apparently thought was funny: “This is our ball…it is made of skin.” The morbid joke was followed by two hashtags, #WorldCup and #WorldCup2014.

The militants accompanied the tweet by also posting a full video of the murder, in which they knock on the off-duty policeman’s door in the middle of the night, then handcuff and blindfold him before slicing his head off.

The video and tweet were part of what has been an all-out ISIS propaganda campaign using social media to terrorize Iraqis, and it appears that the gruesome effort is working. The militants have also posted videos of themselves murdering civilians in drive by shootings and other atrocities. In one video, the insurgents are seen kidnapping a pro-government militia member and the man’s two sons.

In the video, the ISIS militants force the man and the two boys to dig their own graves. The militants then slit their throats.

One of the militants addresses the camera, saying — using the name of pro-government militia Sahwa, “I advise whoever is with the Sahwa to repent and quit.”

The terrifying social media campaign has achieved its purpose. As the militants have advanced, Iraqi security forces have fled in terror, often putting up little or no resistance.

According to U.N. Human Rights official Navi Pillay, the ISIS insurgents have been rounding up civilians, as well as soldiers, and slaughtering them by the dozens. In Mosul, Iraq’s second-largest city, they murdered 17 civilians on a single street, Pillay said.

United States President Barack Obama has ruled out sending U.S. ground troops back into Iraq after they left in 2011, following eight years in Iraq after the 2003 U.S. invasion, but he said the U.S. is considering other options to help bring the ISIS insurgent advance to a halt.