“Never again war!” Leo said from the loggia of St Peter’s Basilica.

Leo, the first American pope, also noted that Sunday was Mother’s Day in many countries and wished all mothers, “including those in heaven” a Happy Mother’s Day.

The crowd, filled with marching bands in town for a special Jubilee weekend, erupted in cheers and music as the bells of St Peter’s Basilica tolled.

It was the first time that Leo had returned to the loggia since he first appeared to the world from there on Thursday night following his remarkable election as pope, the first from the United States. Then too he delivered a message of peace.

Earlier on Sunday, Leo celebrated a private Mass near the tomb of St Peter with head of his Augustinian order, the Reverend Alejandro Moral Anton.

The Mass occurred in the grottoes underneath St Peter’s, the traditional burial place of St Peter, the apostle who is considered the be the first pope.

The area, which is normally open to the public, also contains the tombs of past popes, including Pope Benedict XVI.

Leo on Saturday prayed before the tomb of Pope Francis, located across town at the St Mary Major Basilica.

The 69-year-old Chicago-born missionary was elected 267th pope on Thursday following the April 21 death of Francis.

St Peter’s Square was packed with pilgrims, well-wishers and the curious, many holding up flags from their homelands. Leo gave many special groups a shoutout.