US President Donald Trump met the heads of European Union institutions in Brussels today ahead of a summit of NATO leaders at the military alliance's headquarters in the city later in the day.

Trump, on the fourth leg of his first foreign trip since taking office, was greeted by European Council President Donald Tusk, a former Polish prime minister who chairs meetings of the 28 EU leaders. Also joining the talks will be the bloc's chief executive, European Commission President Jean-Claude Juncker.

EU officials believe Trump has heard other, more positive assessments of the EU's value to Washington since he took office in January

Top European Union officials meeting him for the first time will push cooperation on global trade and fighting climate change as they try to show that the bloc should matter to the United States.

But Donald Tusk and Jean-Claude Juncker, who run the EU's main political institutions in Brussels, expect a less fraught encounter than they might have done a few months ago when Trump was praising Britain for its shock decision to quit the EU and forecasting other countries would follow suit.

Not only do EU officials believe Trump has heard other, more positive assessments of the EU's value to Washington since he took office in January, but the failure of anti-EU nationalists in recent Dutch and French elections had bolstered the bloc.

"Since the first contacts ... much has changed in the EU," a senior EU official said on Wednesday, referring to unpromising and brief discussions with Trump early in the year.

"After the Dutch and the French elections we are in a completely different place in the EU and I think this is the starting point of this discussion."

In January, Tusk referred to Trump as a "threat" to the world order alongside Russia, China and radical Islam. The EU will again press the new president, on his first trip abroad, not to roll back on transatlantic efforts to promote free trade or on US commitments to reduce carbon dioxide emissions.

The EU pair will see Trump again at a G7 gathering in Sicily tomorrow.