Already edgy following a series of terrorist attacks, Christians living in Belgium expressed outrage when a video recording circulated online showing a young Muslim man chanting "Allah, kill the despicable Christians! Allah, kill each and every last one of them!"

According to Haaretz, the video was recorded during the month of Ramadan this year (June 6-July 6) but was not translated until after the murder of French priest Jacques Hamel at the hands of Islamic State (ISIS) supporters in Normandy, France last July 26.

When the Middle East Media Research Institute (MEMRI) provided an online translation of the video, it sparked an outcry in Belgium and prompted a police investigation after Belgian Immigration Minister Theo Francken accused a Muslim cleric of instigating the call to violence.

Police found out that the man in the video is the 16-year-old son of Imam Sheikh Alami, a local radical cleric with Dutch and Moroccan citizenship. Alami was subsequently issued a deportation order for inciting young people to join ISIS.

"It's obvious that his father, the imam, is promoting such ideas not just to fighters to join the battle in Syria, but also to his own children. The young man who appears in the video reflects the father's views, and I understand and empathise with the great concern that city residents have over this," Francken said.

Christians all over Europe have been on high alert over terror attacks since the murder of the French priest during morning mass at his Rouen church.

In Belgium, dozens of suspects have been arrested following suicide bombings in March that left 32 people dead, according to the Wall Street Journal.

Last Aug. 12, two female police officers were attacked with a machete by a 33-year-old Algerian man who was shot and later died of his wounds. ISIS claimed responsibility for both the March suicide bombings and the machete attack.

The ISIS has been encouraging sympathisers to carry out lone-wolf attacks targeting civilians, which authorities have acknowledged are much harder to prevent.

Some of the more recent attacks linked to ISIS in Europe have been carried out away from the more heavily guarded capitals—including the July 14 attack in Nice, in southern France; the July 24 suicide bombing in Ansbach, Germany, and the July 26 killing of Hamel in Normandy.