Pope Francis called for peace and "fraternity" and Queen Elizabeth II warned against "tribalism", as millions across the world celebrated Christmas on Tuesday -- after US President Donald Trump caused a festive furore by raising doubts about Santa Claus's existence during a call with a child.
Some 50,000 worshippers gathered at the Vatican to hear the pontiff's sixth "Urbi et Orbi" (To the City and the World) message appealing for peace in conflict zones such as Syria and Yemen, which face humanitarian crises.
"My wish for a happy Christmas is a wish for fraternity," he told pilgrims in Saint Peter's Square on Tuesday, when Christians celebrate the birth of Jesus Christ.
"Fraternity among individuals of every nation and culture. Fraternity among people with different ideas... Fraternity among persons of different religions."
Francis, the head of the world's 1.3 billion Catholics, had used his mass on Monday night to urge people to curb "insatiable greed".
The pontiff said he hoped a truce in conflict-ravaged Yemen would end a devastating war that has killed around 10,000 people since 2015 and pushed 14 million Yemenis to the brink of famine.
The pope also spoke of the war in Syria, which has forced millions from their homes and reduced swathes of the country to rubble.
He called for a "political solution" to the conflict "so that the Syrian people, especially all those who were forced to leave their own lands and seek refuge elsewhere, can return to live in peace in their own country".
Francis also said he hoped for renewed peace talks between the Israelis and Palestinians "that can put an end to a conflict that for over 70 years has rent the land chosen by the Lord to show his face of love."
Bethlehem in the occupied West Bank, located near Jerusalem but cut off from the city by Israel's separation barrier, has seen an increase in visitors this season after several down years because of the Israeli-Palestinian conflict.
Palestinian tourism officials and hotel operators have reported their strongest season in years.
"This year is much more calm, much better than last year," said Abeer Nasser, a Palestinian from the nearby town of Beit Sahour celebrating in Bethlehem with her son and daughter.
Beyond Bethlehem, Christians worldwide were marking Christmas, with services held from Indonesia to Iraq.
This year's celebrations come after a year of tumult, much of it coming from Washington, where the festive spirit was dampened when the national Christmas tree went dark due to a US government shutdown -- though it ultimately reopened thanks to private donations.
One festive service not affected was the military's annual Santa Claus "tracker", which sees North American Aerospace Defense Command (NORAD) deliver live updates on his international gift delivery route.
Fielding calls from children anxious to know if their presents would arrive on time, Trump risked a spell on Santa's naughty list by telling one child that believing in the jolly man in red at age seven was "marginal".
Entrenching the unfestive tone on Christmas morning, Trump used a news conference following his annual holiday call to US troops to reel off a laundry list of complaints, including his disdain for the US Federal Reserve and the opposition Democrats, whom he blames for the shutdown.
"It's a disgrace what's happening in our country. But other than that, I wish everybody a very Merry Christmas," the president said.
In Bethlehem, visitors were able to view the Church of the Nativity's newly restored mosaics dating to the Crusader era after a major renovation.
Visitors from across the world gathered in the "little town" on Christmas Eve for midnight mass, queueing to see the grotto where Jesus is believed to have been born and taking in a festive parade.
While for many who celebrate the festival Christmas is a time to gather with loved ones, many were struggling with unforeseen events and hardships.
At a little church just outside Indonesia's tsunami disaster zone, a few dozen congregants gathered on Christmas day to pray for the victims.
The tsunami, triggered by a volcanic eruption, left more than 400 people dead when it smashed into popular beaches on southern Sumatra and the western edge of Java, inundating tourist hotels and coastal settlements.
"This Christmas is different because we're celebrating it during a disaster," Rahmat Carita congregant Eliza told AFP.
"For me, it's a chance to contemplate. God's love is real, we must not forget that."
Queen Elizabeth II warned of religious "tribalism" in a Christmas message delivered against a backdrop of Britain bickering over its impending exit from the EU.
The tone of the 92-year-old monarch's annual TV appearances reflected a sombre mood sweeping the island nation as it ponders the perils of leaving the European project after 46 years.
"Even the power of faith, which frequently inspires great generosity and self-sacrifice, can fall victim to tribalism," Elizabeth said.
Spain's second-largest city Barcelona was meanwhile on alert after the US State Department warned of the risk of a terrorist attack during the Christmas holidays.
And in France, groups of "yellow vest" anti-government demonstrators are spending Christmas day at makeshift protest camps on roundabouts across the country, eating devilled eggs and foie gras with new friends they have made in weeks of rallies against the policies of President Emmanuel Macron.