At least 13 persons were killed in an explosion at a Coptic Church in Tanta city of northern Egypt on Palm Sunday.The blast that targeted St George's Coptic Church also left 40 people injured, the BBC reported.The cause of the explosion is not yet known but Egypt's Christian minority has often been targeted by Islamist militants in recent years.In December last year, 25 people died when a bomb exploded at a Coptic cathedral in Cairo during a service.Egypt has seen a wave of attacks by militants since 2013 when the military overthrew President Mohammed Morsi, an elected leader who hailed from the Muslim Brotherhood, and launched a crackdown against Islamists.Some of Morsi's supporters blamed Christians for supporting the overthrow.The explosion occurred as Coptic Christians were celebrating Palm Sunday, one of the holiest days in the Christian calendar, marking the triumphal entry of Jesus Christ into Jerusalem.