WASHINGTON - The White House confirmed on Tuesday that President Donald Trump will join fellow NATO leaders for a key May summit in Brussels, as the US administration seeks to quash questions about Trump's support for the alliance.

The Trump administration has been scrambling to reaffirm its commitment to Washington's military alliances - including NATO - after the Republican billionaire called into question their usefulness during the presidential race.

News that Secretary of State Rex Tillerson would skip a NATO meeting in April - but travel to Russia the same month - did little to allay concerns.

By confirming Trump's participation in the May 25 summit, the US administration - the leading partner in the North Atlantic alliance - moved to reset the narrative.

"The president looks forward to meeting with his NATO counterparts to reaffirm our strong commitment to NATO, and to discuss issues critical to the alliance, especially allied responsibility-sharing and NATO's role in the fight against terrorism," said a White House statement.

Likewise, NATO officials struck a forward-looking note, playing down the apparent snub by Tillerson and instead confirming the summit date and announcing that its Secretary General Jens Stoltenberg - who was in Washington this week - would return to the US capital for talks with the president ahead of the leaders' summit.

The White House said the April 12 meeting would be a chance for Trump and Stoltenberg to "talk about how to strengthen the alliance to cope with challenges to national and international security."

The summit itself, NATO said, would focus on "the alliance's role in the fight against terrorism, and the importance of increased defense spending and fairer burden-sharing" - language that appeared to acknowledge Trump's repeated complaint that US allies are not paying their way.

Just last week, after meeting Chancellor Angela Merkel at the White House, Trump took to Twitter to claim that Germany owes "vast sums of money to NATO and the United States."

Trump's Defense Secretary James Mattis, a former Marine general, has declared that the United States fully supports NATO. Tillerson traveled last week to Asia to reaffirm ties with allies Japan and South Korea.

But regardless of Trump's attendance at the May summit, his top diplomat's absence from its foreign ministers' meeting on April 5 and 6 will be noted with concern, especially by newer East European members on its exposed east flank.