US president Donald Trump has delivered a blunt message to European members of NATO that they must spend more on defence to meet the threat from terrorism.
In a speech in Brussels in front of NATO leaders, Mr Trump said that the failure of member states to meet target to spend 2% of GDP on defence was "not fair to the people and taxpayers of the United States".
Mr Trump is attending a summit of the organisation he once called "obsolete" for the first time as US President.
He claimed that many NATO nations "owe massive amounts of money" from past under-spending on defence, and said that the 2% target was a "bare minimum", which should be raised to enhance the alliance's readiness to deal with modern threats.
In the wake of Monday's terror attack in Manchester, Mr Trump said that NATO must in future focus more closely on "terrorism and immigration" alongside its traditional role of countering threats from Russia.
"Terrorism must be stopped in its tracks or the horror we saw in Manchester and so many other places will continue forever," he said.
"You have thousands and thousands of people pouring into our various countries and spreading throughout and in many cases we have no idea who they are.
We must be tough. We must be strong. And we must be vigilant
"The NATO of the future must include a great focus on terrorism and immigration, as well as on threats from Russia and on NATO's eastern and southern borders."
He added: "These grave security concerns are the same reason I have been very, very direct with Secretary Stoltenberg and members of the alliance in saying that NATO members must finally contribute their fair share and meet their financial obligations.
"For 23 of the 28 member nations are still not paying what they should be paying and what they are supposed to be paying for their defence.
"This is not fair to the people and taxpayers of the United States and many of these nations owe massive amounts of money from past years and not paying in those past years.
"Over the last eight years, the United States spent more on defence than all other NATO countries combined.
"If all NATO members had spent just 2% of their GDP on defence last year we would have another $119 billion for our collective defence and for the finance of additional NATO reserves.
"We should recognise that with these chronic underpayments and growing threats, even 2% of GDP is insufficient to close the gaps in modernising readiness and the size of forces. We have to make up for the many years lost.
"2% is the bare minimum for confronting today's very real and very vicious threats.
"If NATO countries made their full and complete contributions, then NATO would be even stronger than it is today, especially from the threat of terrorism."
Leaders including French President Emmanuel Macron, Luxembourg prime minister Xavier Bettel and Belgian PM Charles Michel were seen to whisper to one another as Mr Trump made his remarks.
Alongside the US, Poland, Greece and Estonia, the UK is one of only five of the 28 Nato members to meet the 2% target, with the US far outspending its partners and providing more than half of the alliance's defence spending.
Mr Trump's comments came after British Prime Minister Theresa May urged NATO allies to "take responsibility" on defence spending.
She also backed Mr Stoltenberg's call for the alliance to join the US-led coalition against the self-proclaimed Islamic State group.
Mr Trump is also set to unveil a memorial to both the 11 September 2001 attacks and to NATO's core Article 5 collective defence guarantee, before a dinner with his fellow 27 leaders.
Earlier, he met the heads of European Union institutions in Brussels on the fourth leg of his first foreign trip since taking office in January.
He was greeted by European Council President Donald Tusk, a former Polish prime minister who chairs meetings of the 28 EU leaders.
Trump shoves fellow NATO leader aside on his first summit
A video of President Trump muscling himself to the front of the world stage at the NATO summit has gone viral.
Footage showing the leaders caught Mr Trump pushing his way past the Prime Minister of Montenegro, then confidently adjusting his suit as he emerged in the front of the group, closer to NATO head Jens Stoltenberg.
Donald Trump pushes his way to front of world leaders at NATO summit pic.twitter.com/RknwGQeKTg
— RTÉ News (@rtenews) May 25, 2017
White House spokesman Sean Spicer, asked about Mr Trump moving past Dusko Markovic, said he had not seen the video but assumed the US president was moving to his designated spot.
The NATO mission of Montenegro, which is joining the Western military alliance against stiff opposition from Russia, did not immediately respond to a request for comment.
The small Balkan country will formally become NATO's 29th state in June but Mr Markovic joined the Brussels summit, Mr Trump's first, and a ceremonial opening of the alliance's new headquarters.
During the leaders' joint photo shoot in the new building, Canadian Prime Minister Justin Trudeau encouraged his counterparts to wave for the cameras. Some did as he requested, but Mr Trump did not raise his arm.
Mr Trump smiled briefly, but otherwise kept a serious expression on his face for the brief session.
