U.S. Attorney General William Barr has reportedly told people close to him that he could resign, after his call for President Donald Trump to stop tweeting about Justice Department cases and personnel was ignored.

The Washington Post and Associated Press reported Barr – hitherto a staunch ally of the president – had privately told officials he may quit the post days after saying in an ABC News interview that Trump's tweets make it "impossible" for him to do his job.

There has been skepticism over the intent of the interview, and it remains unclear how seriously the quit threat is. Barr's spokeswoman said late on Tuesday that the attorney general "has no plans to resign."

Barr has told people close to Trump about his concerns, the Washington Post reported, but it was not immediately clear if the attorney general had told his boss directly.

"He has his limits," the newspaper quoted one person familiar with Barr's thinking as saying.

Barr may be sharing his position in the hope the president gets the message and stops tweeting about the Justice Department's criminal investigations, the Post added.

Trump insisted on Tuesday he had total confidence in Barr. "I do make his job harder ... I do agree with that," the president told reporters. "The attorney general is a man with great integrity."

However, Trump also tweeted on Tuesday that he may sue those involved in special counsel Robert Mueller's Russia investigation and made further comments about Roger Stone, the president's longtime confidante who has been convicted of witness tampering and obstruction.

Last week senior Justice Department officials withdrew an earlier sentencing recommendation for Stone, who was found guilty in November of seven counts of lying to Congress, prompting upheaval within the department.

Trump has used Twitter to attack the four prosecutors who had argued the case as well as the judge presiding over it.

More than 1,000 former department officials have called for Barr to resign.

(With input from agencies)