Trump faces rougher reception in NATO, EU meetings

After a warm welcome in the Middle East and a "fantastic" visit with the pope, U.S. President Donald Trump walks on shakier ground on Thursday when European Union and NATO leaders will press him on defence, trade, and environmental concerns.

The Republican president, midway through his first foreign trip since taking office, has basked in the glow of favourable receptions in Riyadh and Jerusalem, where leaders lauded his harsh words for Iran.

Praise may be in shorter supply in Brussels.

Trump questioned the relevance of the NATO military alliance as a presidential candidate, and is considering pulling the United States out of the Paris agreement on climate change - a huge concern in Europe. The EU was also a party to the Iran nuclear agreement, which Trump has criticized sharply.

"We expect him to recommit to NATO's founding rule that an attack against one ally is an attack against all," said a senior European diplomat at the North Atlantic Treaty Organization.

"Words matter and there is a huge expectation on that."

Trump will also meet Europe's chief executive Jean-Claude Juncker and European Council President Donald Tusk, who chairs EU summits, in the morning.

He will then go to NATO's new, billion-dollar headquarters where he will unveil a memorial to the Sept. 11, 2001, attacks on New York and Washington.