Pope Benedict XVI called for an "end to the bloodshed" in Syria and denounced the "savage" violence in Africa on Tuesday, even as Nigeria witnessed a Christmas attack on Christians.
Speaking in his traditional Christmas message, the pope touched on several other of the world's conflict zones.
A capacity crowd of 40,000 pilgrims filled the vast St Peter's Square to hear the 85-year-old pope, resplendent in red vestments, deliver the "Urbi et Orbi" (To the City and to the World) message.
Speaking from the balcony of St Peter's Basilica, the pope called for a return to peace in Nigeria, where he said "savage acts of terrorism continue to reap victims, particularly among Christians."
As he spoke, news was filtering in of a deadly attack there.
Gunmen attacked a church in the northern state of Yobe during a Christmas Eve service, killing six people, including the pastor, before setting the building ablaze.
It was the latest attack blamed on the radical Islamist sect Boko Haram, which has repeatedly targeted churches during times of worship, including multiple attacks last year on Christmas Day.
The pope also prayed for peace in Syria, whose people have been "deeply wounded and divided by a conflict which does not spare even the defenceless and reaps innocent victims."
In a message watched by millions around the world, he called "for an end to the bloodshed... and dialogue in the pursuit of a political solution to the conflict."
His wide-ranging speech pressed for peace in the Middle East and appealed to China's new leadership to respect religious freedom there.
In Indonesia, more than 200 Muslims threw rotten eggs at Christians wanting to hold a Christmas mass outside Jakarta, police said.
Around a hundred Christian worshippers had gathered for the mass near the spot where they hoped to build a church but saw the project barred by district government and community members.
At the midnight mass in Bethlehem, the most senior Roman Catholic bishop in the Middle East issued a special call for efforts to resolve the Israeli-Palestinian conflict.
"Only justice and peace in the Holy Land can reestablish balance and stability in the region and in the world," Patriarch Fuad Twal told worshippers in the West Bank city, the traditional birthplace of Jesus.
"From this holy place, I invite politicians and men of good will to work with determination for peace and reconciliation that encompasses Palestine and Israel in the midst of all the sufferings in the Middle East," Twal said.
The outgoing archbishop of Canterbury, in his final Christmas Day sermon, acknowledged that last month's failure by England's state church to approve women bishops had been "deeply painful."
The decision had damaged the church's reputation, Rowan Williams, who steps down at the end of the year, said from Canterbury Cathedral in southeast England.
The liberal Williams, head of the world's 80 million Anglicans, fought over the last decade to bridge the divide with the church's traditionalists.
In South Africa, former leader Nelson Mandela shared Christmas greetings with visitors to his hospital bedside, including his wife Graca Machel, other family members and President Jacob Zuma.
"We found him in good spirits," Zuma said. "He was happy to have visitors on this special day and is looking much better."
The 94-year-old anti-apartheid icon was admitted on December 8 to a Pretoria hospital where has been treated for a recurrent lung infection and had surgery to remove gallstones.
Former US president George H.W. Bush celebrated Christmas in a Texas hospital with his family after a series of health setbacks delayed his release. He has been suffering from bronchitis.
Britain's Margaret Thatcher, 87, was also confined to a hospital bed for Christmas this year.
The former prime minister was admitted to hospital on Thursday for a minor operation to remove a growth in her bladder.
Also in Britain, Prince William and his pregnant wife Catherine were absent when the royal family attended a Christmas church service.
William and the former Kate Middleton, who is recovering from severe morning sickness that landed her in hospital for four days earlier this month, broke with tradition to spend Christmas Day with her family rather than the royals.
The 86-year-old queen, who had missed church on Sunday due to a cold, appeared in good spirits as she arrived for the service at her Sandringham estate in Norfolk, eastern England.
In her Christmas message, she paid tribute to the athletes and volunteers who helped make the Olympic and the Paralympic Games a success, and said it had been "humbling" to see vast crowds joining celebrations marking her 60th year on the throne.
In the United States, the organisation responsible for monitoring North American airspace helped children track Santa Claus's progress as he completed his whirlwind journey around the globe.
The Santa tracker set up by the North American Aerospace Defense Command (NORAD), a US-Canada joint operation, said Father Christmas and his hardworking reindeer were resting at the North Pole, having delivered more than seven billion gifts during his annual journey.