Al-Azhar Observer for Combating Extremism said in a statement that it "condemns this sinful terrorist attack against the two churches and their priests and the shedding of innocent blood."

A man, reportedly a 25-year-old Moroccan, stormed into two churches in the southern Spanish city of Algeciras armed with a machete on Wednesday evening, killing a verger at one church and badly injuring a priest at the other.

Police arrested the attacker at the scene and Spanish prosecutors immediately opened a terror probe into the incident.

The mayor of Algeciras has declared a day of mourning and called residents to gather for a demonstration of condemnation at midday (11:00 GMT) in front of the church where the verger, Diego Valencia, was killed.

“Al-Azhar observer had warned of possible terrorist attacks in Europe by lone wolves, who are an easy choice for terrorist groups to carry out their plans to spread panic among the citizens of these countries and threaten peace,” the statement said.

“The observer warns of the occurrence of more attacks as terrorist organisations continue to indoctrinate their lone wolves with thoughts of revenge and extremist ideologies," the statement said.

The Observer stressed that “Islam is innocent of every despicable terrorist act that targets innocents, especially in unsuspecting places of worship,” describing the incident as an “act of brutal terrorism from which all religions are innocent.”

The observer was created in 2015 by Al-Azhar, the world’s oldest institution of Sunni Islamic learning, to monitor and respond to erroneous and extremist interpretations of Islam.

The observer also issues periodic reports to monitor and assess the attacks and movements of terror groups in various regions of the world.