Iraqi Christians in Bartella have celebrated their first Christmas mass in the town since it was captured by the Islamic State group in 2014.

Once home to thousands of Assyrian Christians, Bartella emptied in August 2014 when stronghold Mosul fell to the militant group's blitz across large parts of Iraq and neighbouring Syria.

Iraqi forces took it back in the first few days of the US-backed offensive that started in October.

Bartella is in the region of Nineveh, one of the most ancient settlements of Christianity, going back nearly 2,000 years.

Pope calls for more humility

Pope Francis kisses a statue of baby Jesus during Christmas night Mass in Saint Peter's Basilica. ( Reuters: Tony Gentile )

Pope Francis said Christmas has been "taken hostage" by dazzling materialism that puts God in the shadows and blinds many to the needs of the hungry, the migrants and the war weary.

"If we want to celebrate Christmas authentically, we need to contemplate this sign — the fragile simplicity of a small newborn, the meekness of where he lies, the tender affection of the swaddling clothes. God is there," the Pope said at St Peter's Basilica.

At the service, attended by some 10,000 people as well as dozens of cardinals and bishops, Pope Francis said the many in the wealthy world had to be reminded that the message of Christmas was humility, simplicity and mystery.

"Jesus was born rejected by some and regarded by many others with indifference," he said.

"Today also the same indifference can exist, when Christmas becomes a feast where the protagonists are ourselves, rather than Jesus; when the lights of commerce cast the light of God into the shadows; when we are concerned for gifts, but cold toward those who are marginalised."

Francis has spent much of this year bemoaning the Islamic extremist violence that has driven Christians from Mideast communities that date to the time of Christ, demanding countries do more to welcome refugees.

Obamas deliver final White House Christmas message

Sorry, this video has expired 'Care for the sick, feed the hungry, welcome the stranger': Obamas share final Christmas message

Barack Obama has delivered his final Christmas message as President of the United States, joined by his wife Michelle to remember Jesus' message of "boundless love and compassion".

"The idea that we are our brother's keeper and our sister's keeper, that we should treat others as we want to be treated. That we care for the sick, feed the hungry, welcome the stranger, no matter where they come from or how they practice their faith," Mrs Obama said.

The Obamas thanked the country's troops and reflected on the couple's eight years in the White House.

The official White House video also included a clip of their first Christmas message and Mrs Obama playfully mocked the President's "dad jokes".

Canada's Prime Minister Justin Trudeau, whose birthday is on Christmas Day, released video messages on Twitter, reminding Canadians to reach out to those who are struggling the most.

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Faithful mark Christmas in Bethlehem

Thousands of pilgrims and tourists from around the world, together with local Christians, gathered in the biblical town of Bethlehem to celebrate Christmas eve in the traditional birthplace of Jesus.

Despite tightened security, the faithful braved the chilly weather outside the town's Manger Square as traditional Christmas songs like "Jingle Bells" played in Arabic over loudspeakers and scout groups paraded with bagpipes and sang carols.

Sharolyn Knight, a 28-year-old teacher from Georgia, said she was in Bethlehem for the first time and experiencing mixed emotions.

"It's been sobering and humbling because it's a place with a lot of heavy stuff, religious and historical. At the same time, disillusioning because there is so much strife in the place where Jesus was born."

The Christmas festivities brought a boost of holiday cheer to Christians in the Holy Land, who make up just a small percentage of the population.

The region has experienced a wave of Israeli-Palestinian bloodshed that erupted over a year ago. The violence has tapered off in recent months, but has not halted completely.

Rula Maaya, the Palestinian Minister of Tourism, said all the hotels in Bethlehem were fully booked.

"All people over the world are looking at Bethlehem so we hope more and more tourists will come during the year and that next year we will celebrate Christmas without occupation," he said.

A Christian worshipper prays after lighting a candle on Christmas Eve at the Church of the Nativity in Bethlehem. ( AP: Majdi Mohammed )

Tight security for Christmas in Europe

Authorities tightened security for the Christmas weekend in Italy after police killed the man believed to be responsible for the Berlin market truck attack, while other European cities kept forces on high alert.

In France, where Islamist militants killed 130 people in shooting and bomb attacks in Paris in November 2015, authorities said more than 91,000 policemen and soldiers would be deployed, with additional security measures being enforced at churches.

Emergency rule has been in place since the Paris attacks, and French soldiers patrol the capital's streets.

French Police officers patrol near Notre Dame Cathedral as worshippers arrive for the Christmas Eve mass in Paris. ( AP: Francois Mori )

In Germany, federal police reinforced armed patrols at airports and rail stations, officials said, as well as reintroducing spot checks along a 30-km corridor inside the international frontiers.

Britain is on its second-highest threat level, meaning an attack by militants is considered highly likely.

Police there have increased security at a number of popular tourist attractions, including around Queen Elizabeth's London residence, Buckingham Palace.

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