Pope Francis, who is scheduled to visit Egypt later this month, decried Sunday's blast at a Coptic Church in Egypt's Nile Delta that killed 21 worshippers and wounded dozens more.
At the end of his Palm Sunday Mass, the leader of the world's Roman Catholic Church said, " I pray for the dead and the victims. May the Lord convert the hearts of people who sow terror, violence and death and even the hearts of those who produce and traffic in weapons."
Earlier, in his homily, Francis denounced the suffering in the world today.
He said those who " . . . suffer from slave labor, from family tragedies, from diseases . . . They suffer from wars and terrorism, from interests that are armed and ready to strike."
Before the beginning of the Mass, Francis and a group of cardinals, holding elaborately braided palm fronds, walked through the crowd at Saint Peter's Square.
In Jerusalem, worshippers at the Church of the Holy Sepulcher celebrated Palm Sunday by waving palm branches during the procession next to the newly restored Tomb of Jesus.
The church in Jerusalem's Old City is believed to be the burial site of Jesus.
Palm Sunday marks Jesus' triumphant entry in Jerusalem more than 2,000 years ago and the beginning of the Christian Easter Holy Week.