WASHINGTON (NYTIMES) - FBI Director James Comey asked the Justice Department over the weekend to publicly reject President Donald Trump's assertion that former president Barack Obama ordered the tapping of Trump's phones, senior US officials said .

Comey has argued that the highly charged claim is false and must be corrected, they said on Sunday (March 5), but the department has not released any such statement.

Comey, who made the request on Saturday after Trump levelled his allegation on Twitter, has been working to get the Justice Department to knock down the claim because it falsely insinuates that the FBI broke the law, the officials said.

A spokesman for the FBI declined to comment. Sarah Isgur Flores, spokesman for the Justice Department, also declined to comment.

Comey's request is a remarkable rebuke of a sitting president, putting the nation's top law enforcement official in the position of questioning Trump's truthfulness.

The confrontation between the two is the most serious consequence of Trump's weekend Twitter outburst, and it underscores the dangers of what the president and his aides have unleashed by accusing the former president of a conspiracy to undermine Trump's administration.

The White House showed no indication that it would back down from Trump's claims. On Sunday, the president demanded a congressional inquiry into whether Obama had abused the power of federal law enforcement agencies before the 2016 presidential election.

In a statement from his spokesman, Trump called "reports" about the wiretapping "very troubling" and said that Congress should examine them as part of its investigations into Russia's meddling in the election.

Along with concerns about the potential attacks on the bureau's credibility, senior FBI officials are said to be worried that the notion of a court-approved wiretap will raise the public's expectations that federal authorities have significant evidence implicating the Trump campaign in colluding with Russia's efforts to disrupt the presidential election.

One problem Comey has faced is that there are few senior politically appointed officials at the Justice Department who can make the decision to release a statement, the officials said.

Attorney General Jeff Sessions recused himself on Thursday from all matters related to the federal investigation into connections between Trump, his associates and Russia.

Comey's behind-the-scenes manoeuvering is certain to invite contrasts to his actions last year, when he spoke publicly about the Hillary Clinton e-mail case and disregarded Justice Department entreaties not to.

It is not clear why Comey did not issue the statement himself. He is the most senior law enforcement official who was kept on the job as the Obama administration gave way to the Trump administration. And while the Justice Department applies for intelligence-gathering warrants, the FBI keeps its own set of records and is in position to know whether Trump's claims are true.

While intelligence officials do not normally discuss the existence or non-existence of surveillance warrants, no law prevents Comey from issuing the statement.

In his demand for a congressional inquiry, the president, through his press secretary, Sean Spicer, issued a statement on Sunday that said: "President Donald J. Trump is requesting that as part of their investigation into Russian activity, the congressional intelligence committees exercise their oversight authority to determine whether executive branch investigative powers were abused in 2016."

Spicer, who repeated the entire statement in a series of Twitter messages, added that "neither the White House nor the president will comment further until such oversight is conducted."

A spokesman for Obama and his former aides have called the accusation by Trump completely false, saying that Obama never ordered any wiretapping of a US citizen.

"A cardinal rule of the Obama administration was that no White House official ever interfered with any independent investigation led by the Department of Justice," Kevin Lewis, Obama's spokesman, said in a statement on Saturday.

Trump's demand for a congressional investigation appears to be based, at least in part, on unproven claims by Breitbart News and conservative talk radio hosts that secret warrants were issued authorising the tapping of the phones of Trump and his aides at Trump Tower in New York.

In a series of Twitter messages on Saturday, the president seemed to be convinced that those claims were true. In one post, Trump said, "I'd bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!"

On Sunday, Sarah Huckabee Sanders, deputy White House press secretary, said the president was determined to find out what had really happened, calling it potentially the "greatest abuse of power" that the country has ever seen.

"Look, I think he's going off of information that he's seen that has led him to believe that this is a very real potential," Sanders said on ABC's "This Week" program. "And if it is, this is the greatest overreach and the greatest abuse of power that I think we have ever seen and a huge attack on democracy itself. And the American people have a right to know if this took place."

Trump's demands for a congressional investigation were initially met with skepticism by lawmakers, including Republicans. Appearing on CNN's "State of the Union" on Sunday, Republican Senator Marco Rubio said he was "not sure what it is that he is talking about."

"I'm not sure what the genesis of that statement was," he said.

Pressed to elaborate on "Meet the Press", Rubio said: "I'm not going to be a part of a witch hunt, but I'm also not going to be a part of a cover-up."