Pope Francis appeared before some 150,000 pilgrims massed in St. Peter's Square on Sunday for his first Angelus prayer and asked the faithful to pray for him.

"Thank you for your welcome, and for your prayers," the first pope from Latin America told the cheering crowd from the window of the papal apartment overlooking the square. "Pray for me," he added.

He also urged the world to be more forgiving and merciful and not so quick to condemn other people's failures. "A little bit of mercy makes the world less cold and more just," he said.

Four days after his election, the Argentine pope spoke both as pope and as parish priest - earlier he said Mass for a few hundred Vatican workers in a tiny church just inside the city-state's walls.

Francis also issued his first tweet shortly after performing Angelus prayer. "Dear friends, I thank you from my heart and ask you to continue to pray for me," he tweeted from the @Pontifex account.

The Angelus has traditionally been a moment to comment on international issues, but Francis instead used it to emphasize his Italian roots, saying he chose to name himself after St. Francis of Assisi because of his "spiritual ties with this land."

Earlier Sunday the pope grabbed an opportunity to shake hands with well-wishers lining up outside a nearby Vatican gate.

AFP - Reuters