In his Christmas message, the Pope appeals for peace and speaks about terrorism.

Reuters Pope Francis on Sunday appealed for peace at Christmas in a world torn apart by war and terrorism, asking people to remember migrants, refugees and those affected by economic instability caused by the "idolatry of money".

Pope Francis, in his fourth Christmas season since his election in 2013, also called on Palestinians and Israelis, facing renewed tensions after a United Nations resolution condemning Israeli settlements in occupied territory, to have the courage to put aside hatred and revenge and "write a new page in history."

His traditional "Urbi et Orbi" (to the city and the world) message was driven by war, violence, and suffering in a time that should have been defined by harmony and peace, symbolized by the baby Jesus.

"Peace to those who have lost a loved one as a result of brutal acts of terrorism, which have sown fear and death in the hearts of so many countries and cities," he told some 40 people gathered in St. Peter's Square.

Security was reinforced for Christmas week in Italy and the Vatican after Italian police killed the man believed to be responsible for the Berlin supermarket attack, while other European cities kept their forces on high alert.

"Today this message (of peace) goes to the ends of the earth to reach all people, especially those marked by war and harsh conflicts that seem stronger than the yearning for peace," he said, speaking in Italian from the central balcony of St. Peter's Basilica.

He called for peace in Syria, urging immediate assistance for the exhausted population of the city of Aleppo, which Syrian government forces recaptured last week after four years of devastating fighting with rebels.

"It is time for the weapons to be laid down forever (in Syria), and for the international community to actively seek a negotiated solution so that civil coexistence can be restored in the country," he said.

Pope Francis, the first Latin American Pope, also stated that Christmas should inspire everyone to help the less fortunate, including migrants, refugees, and those swept up by economic and social upheavals.

"Peace to the people who suffer because of the economic ambitions of a few, because of pure greed and the idolatry of money, which leads to slavery," he said.

In his Christmas Eve Mass on Saturday, Francis said the holiday had been "held hostage" by the blinding materialism that relegates God to the shadows.

On Sunday, he also called for an end to "fundamentalist terrorism" in Nigeria, referring to Boko Haram, which has killed 15 people and displaced more than two million during a seven-year insurgency to create an Islamic state.

Pope Francis also called for an end to tensions between the government and the opposition in Venezuela, for harmony in Colombia, which recently ended a civil war with the FARC, and for an end to the fighting on the Korean peninsula and in Myanmar.