Washington: US President Donald Trump's promise to a foreign leader troubled an official in the US intelligence community so much that it prompted them to file a whistleblower complaint", the Washington Post reported on Wednesday.

US President Donald Trump. Credit:Bloomberg

The Post, which cited two former officials familiar with the matter, said it was not immediately clear which foreign leader Trump was speaking with or what he pledged to deliver. The communication was a phone call, one former official said, according to the Post.

Intelligence Community Inspector General Michael Atkinson determined that the complaint was credible and troubling enough to be considered a matter of "urgent concern", a legal threshold that requires notification of congressional oversight committees, the Post said.

But the acting Director of National Intelligence Joseph Maguire has refused to share details about the complaint with lawmakers, the Post reported.