WASHINGTON (Reuters) - A complaint by a former US intelligence officer who worked at the White House over President Donald Trump is centered on Ukraine, acting US National Intelligence Director Joseph Maguire declined to disclose to Congress the nature of the complaint.

The Washington Post and The New York Times, citing informed sources, said President Trump spoke with his Ukrainian counterpart Vladimir Zelinsky two and a half weeks before the complaint was due.

House Democrats opened an investigation this month to consider whether Trump and his private lawyer tried to influence the Ukrainian government to help the president in his re-election campaign.

It is noteworthy that the Inspector General of Intelligence agencies Michael Atkinson made a closed statement to the Committee on Intelligence in the House of Representatives and refused to disclose the contents of this complaint.

Trump responded
Trump responded to the accusations in a tweet on Twitter. "This story is not true," he said.

Trump said it was illogical to talk something improper to a foreign leader during a potentially overcrowded call, saying he had done only what was right and good for the United States.

The Washington Post said Trump had made an "unusual promise" to a foreign leader by telephone, and the call had become the subject of a complaint that had created tension between the intelligence and Congress.

The newspaper quoted two former US officials familiar with the matter as saying that the promise made by Trump during contact with that foreign leader was "disturbing."

They said the alarming situation prompted an intelligence official familiar with the communication to file a complaint with US intelligence inspector General Michael Atkinson on August 12.

Atkinson concluded that the complaint was credible and could be categorized as an issue of urgent importance, requiring that relevant committees of Congress be informed.

But Acting Director of National Intelligence Joseph McGuire protested, refusing to brief lawmakers, sparking a legal and political controversy, and sparking speculation that the intelligence chief is trying to protect Trump.