Tuesday’s explosion at a soccer viewing center in northeastern Nigeria claimed the lives of several men and young boys watching the Brazil-Mexico World Cup match.

A hospital source said Wednesday that 21 people were killed in the explosion and another 27 were injured.

The incident occurred on the outskirts of Damaturu, in Yobe state, the sources said. The explosives had been concealed in an abandoned motorized rickshaw outside the center.

Volatile northeastern Nigeria is the home of the Boko Haram group, the militant Islamists who abducted scores of schoolgirls in April.

A Yobe police official in Damaturu told CNN the extremist group had distributed leaflets to the viewing centers in three different languages warning them not to open during the World Cup.