Footage of the moment when the Pope was knocked down
A shaken Pope Benedict has celebrated Christmas Eve Mass in St Peter's Basilica shortly after being knocked over by a female spectator.
The woman, said to be mentally unstable, managed to grab him by his vestments near the neck as a security guard tried to overwhelm her.
The Vatican said she had also tried to jump at the Pope last year.
French Cardinal Roger Etchegaray, 87, was standing a few metres away and fell and broke his hip during the incident.
Proceeding with the Mass, Benedict looked shaken and stumbled over some words.
The Vatican later said the Pope was unharmed and would give Mass on Christmas Day as planned.
"It was an assault, but it wasn't dangerous because she wasn't armed," said Vatican spokesman Federico Lombardi.
The Holy Father went down and all of a sudden all the security people were all on top of it
Marybeth Burns Eyewitness
The BBC's David Willey, in Rome, says the woman is now undergoing checks at a medical facility in Rome.
Vatican officials named her as 25-year-old Susanna Maiolo and said she held dual Swiss and Italian nationality.
The Christmas Eve service in the Vatican started two hours early because officials did not want the pontiff, 82, to get tired.
Dressed in a red hooded sweatshirt, the attacker leaped over the barrier towards the Pope, prompting gasps from the crowd.
David Willey, BBC News, Rome
The Pope will next year celebrate his 83rd birthday. He is in relatively good health for his age but he was clearly shaken by the incident and stumbled several times over words in his homily.
This was undoubtedly the most serious breach of security inside the Vatican in recent years.
Although the Pope was physically unharmed by this sudden attack, security arrangements at papal ceremonies will have to be urgently reviewed as there was apparently a similar, but unsuccessful, attempt to hurt the Pope last Christmas.
Eyewitness Marybeth Burns, a US tourist, told the Associated Press the woman "sort of flew over the barricade".
"The Holy Father went down and all of a sudden all the security people were all on top of it, you know the whole pile there, getting her off and pulling him back up," she said.
Security officials rushed down the main aisle to detain the woman, who was later arrested by police.
Vatican security staff said they recognised the woman as being the same person who had tried to jump a barricade to get close to the Pope at the same service last year.
The Pope had to be helped up by his master of ceremonies.
The pontiff had earlier appeared briefly at nightfall at the window of his studio to light a candle in a sign of peace.
Meanwhile in Bethlehem thousands of pilgrims saw Latin Patriarch Foud Twal, the most senior Roman Catholic cleric in the Holy Land, deliver his Christmas message.
"The wish that we most want, we most hope for, is not coming - we want peace," he said after arriving in Bethlehem after the traditional holiday procession from nearby Jerusalem.
Festivities in Bethlehem began with a traditional boy scout band and ended with midnight Mass in St Catherine's Church, next to the Church of the Nativity.
Pope Benedict XVI delivered his Christmas Day blessing to a crowd of thousands
Arriving in Bethlehem, the Latin Patriarch said people in the region wanted freedom of movement.
"We don't want walls, we don't want separation fences."
Addressing worshippers, he added: "[This land's] inhabitants are brothers who see each other as enemies.
"This land will deserve to be called holy when she breathes freedom, justice, love, reconciliation, peace and security."
The Mass was said next to a church built over the stall where Mary is believed to have given birth to Jesus.
Some 300 Christians over the age of 35 from the Gaza Strip were given permission by the Israeli military to leave the territory and come to Bethlehem for 24 hours to celebrate Christmas.
A total of 15,000 tourists are expected in the town during this period, in a year that has seen a record number of visitors - some 1.6 million.
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