Pope Francis on Sunday appealed for peace as he kicked off Christmas celebrations with a mass at Saint Peter's Basilica as the Israel-Hamas war raged in the Gaza Strip.

"Tonight, our hearts are in Bethlehem, where the Prince of Peace is once more rejected by the futile logic of war, by the clash of arms that even today prevents him from finding room in the world," the pope said to some 6,500 faithful who attended the traditional service.

Francis's address never mentioned Israel or Gaza by name, but he made numerous references to violence and war. 

arguing that justice would not come "from a show of force", the pontiff said Jesus "does not eliminate injustice from above by a show of force, but from below, by a show of love".

"He does not burst on the scene with limitless power," he said, speaking in Italian with an official translation provided in seven languages.

During his weekly Angelus prayer earlier Sunday, the pope said that "we are close to our brothers and sisters who are suffering from war — we are thinking of Palestine, of Israel, of Ukraine".

On Christmas Day, the pontiff is due to lead the traditional "Urbi and Orbi" prayer at 1100 GMT, during which he normally mentions the conflicts around the world.

A Hamas attack on Israel October 7 left around 1,140 people dead, most of them civilians, according to an AFP tally based on official Israeli figures.

The Palestinian militants also abducted around 250 people, 129 of whom Israel says remain in Gaza.

Israel retaliated with a sustained bombardment and ground invasion of Gaza, where 20,424 people have been killed, mostly women and children, according to the latest toll from the territory's Hamas-run health ministry.

The pope has frequently denounced attacks on civilians in the ongoing conflict. 

With the Gaza war raging, the Christmas celebrations in Bethlehem, where Christians believe Jesus was born, were effectively cancelled on Sunday.

This year the city is almost deserted, with few worshippers around and no Christmas tree erected, after church leaders decided to forego "any unnecessarily festive" celebrations in solidarity with Gazans.