A woman knocked Pope Benedict XVI to the ground after vaulting over security barricades in a dramatic start to Christmas Eve mass at St Peter's Basilica.
Video footage showed the woman in a red sweatshirt leaping over the barricade and grabbing the 82-year-old pope as he began the traditional procession to the altar.
The pontiff emerged unharmed and later delivered his homily, speaking out against selfishness as Christians across the world celebrate the birth of Jesus Christ.
'Conflict and lack of reconciliation in the world stem from the fact that we are locked into our own interests and opinions, into our own little private world,' said the spiritual leader of the world's 1.1bn Catholics.
The woman, described as 'apparently unbalanced' by the Vatican spokesman, was arrested by Vatican police.
In Bethlehem, thousands of pilgrims celebrated Christmas in the traditional birthplace of Jesus, with festivities on a scale unseen since the outbreak of Israeli-Palestinian fighting in 2001.
At midnight mass, the top Roman Catholic cleric in the Holy Land called on the faithful to pray for peace in the troubled region.
'Its inhabitants are brothers who see each other as enemies,' the Latin Patriarch of Jerusalem Fuad Twal told worshippers. 'This land will deserve to be called holy when she breathes freedom, justice, love, reconciliation, peace and security.'
Live rock music mingled with traditional carols in Manger Square as thousands of pilgrims and Palestinians joined the festivities, providing some respite for a town living in the shadow of a huge Israeli-built wall.
'This is the place where God gave us his son, so it is very special for me to be here, for me and my whole community,' said Juan Cruz, 27, from Mexico.
In the United States, a huge winter storm forced scores of churches to cancel Christmas Eve services as blizzards and freezing rain brought treacherous holiday travel conditions for millions.
At least 19 deaths were attributed to the storm system spanning two thirds of the country.
US President Barack Obama left the freeze far behind, starting a family holiday in his native state of Hawaii cheered by a major health reform victory.