Trump vows to push for peace after meeting with Pope Francis

At the Vatican on Wednesday, Donald Trump vowed to use his US presidency to promote global peace, before heading to a high-stakes summit of the world's biggest military alliance.

Meeting for the first time, the president and Pope Francis sidestepped deep differences over issues ranging from the environment to the plight of refugees and the poor.

"Honor of a lifetime to meet His Holiness Pope Francis," a star-struck Trump wrote on Twitter before leaving Rome for Brussels and the next leg of his first overseas trip as US president.

In Brussels, a city he once dubbed a "hellhole," Trump however faced thousands of protesters ahead of his first summit on Thursday with wary leaders of NATO and the European Union.

Trump sparked fears of an end to the transatlantic alliance when he dismissed NATO as "obsolete" while on the campaign trail and mortified the EU by backing Brexit.

Trump said that the most important issue during his time in Belgium was terrorism after the "horrible situation" in Manchester, England, where a suicide bomber killed 22 people in an attack claimed by the Islamic State (IS) group.

"We are fighting very hard, doing very well under our generals. Making tremendous progress," Trump told Belgian Prime Minister Charles Michel.

"But when you see something like what happened a few days ago, you realise how important it is to win this fight. And we will win this fight."

'Fantastic meeting'

Trump left Rome declaring his determination for peace following his keenly anticipated encounter with Pope Francis, the 80-year-old former Jesuit priest who has made championing the poor and the third world major themes of his papacy.

In their world view and tastes, the pontiff who eschews the use of the palaces at his disposal and the luxury hotel tycoon appear worlds apart.

But despite the pope looking initially grim-faced, both men ended up mostly all smiles, relaxed and even jovial.

Accompanied by his wife Melania and daughter Ivanka, Trump met Francis in the private library of the Apostolic Palace, the lavish papal residence that the current pope eschews in favour of more modest lodgings.

"He is something," Trump later said of his host. "We had a fantastic meeting."

There was even a light-hearted moment when Francis made an apparent allusion to Trump's imposing physical size.

"What do you feed him on? Potica?" Francis asked Melania, in a reference to a calorie-laden cake that comes from her native Slovenia and is pronounced "potteezza". Reporters initially thought he said "pizza".

'He called Brussels a hellhole and yet he comes here like a conqueror'

- Protester in Brussels

Trump also told the pope he was committing more than $300m to help prevent or tackle famine in Yemen and several countries in Africa.

The Vatican described the discussions as "cordial" and emphasised the two men's joint opposition to abortion and shared concern for persecuted Christians in the Middle East.

The pope presented Trump with a medallion engraved with an olive tree, the international symbol of peace.

"I give it to you so you can be an instrument of peace," the pope said in Spanish. "We can use peace," Trump replied.

In Brussels, Trump met Belgium's King Philippe and Queen Mathilde and held talks with Michel, while thousands rallied against his policies in the centre of the city.

"Trump not welcome," said banners waved by the crowd, which police said numbered around 9,000. Organisers put the size of the demonstration at 12,000.

"He called Brussels a hellhole and yet he comes here like a conqueror," leftwing protester Yannick Blaise told AFP.

Trump sparked fury by deriding the Belgian capital as a "hellhole" ruined by Muslim immigration in January 2016 - two months before suicide bombers killed 32 people in the city.

The rally filled the central Bourse square of the city just hours after Trump touched down in Air Force One.

On Thursday, he first meets EU President Donald Tusk and European Commission chief Jean-Claude Juncker, having previously backed Britain's shock Brexit vote and saying the EU was a doomed would-be superstate.

He will then hold his first summit with NATO leaders, who are holding out for a public show of Trump's commitment in return for joining the US-led coalition against IS in the wake of the Manchester attacks.

Trump's Vatican visit was the third leg of his overseas trip, after stops in Saudi Arabia and Israel and the Palestinian territories.

The high-profile trip has diverted attention from Trump's domestic pressures over alleged campaign collusion with Russia.