WASHINGTON (NYTIMES) - President Donald Trump is confident that neither his former campaign chairman nor his former national security adviser has damaging information about him to offer prosecutors, a White House lawyer told The New York Times.

"The President has no concerns in terms of any impact, as to what happens to them, on his campaign or on the White House," the lawyer, Ty Cobb, said in an interview on Thursday for The Times' podcast The New Washington.

The Justice Department special counsel, Robert S. Mueller III, is investigating whether anyone close to Trump worked with Russian operatives to disrupt last year's presidential election. He has summoned witnesses before a federal grand jury in Washington to gather information about Paul Manafort, the former Trump campaign chairman; Michael Flynn, the retired general and former national security adviser; and other associates of Trump.

Manafort has been warned to expect an indictment, raising the prospect that Mueller will offer him leniency in exchange for incriminating information about Trump.

Cobb's remarks echo what those around Manafort have said: that he has no such information to offer. Trump has sought to play down the significance of Manafort's role with the campaign.

"He likes and respects Mr Manafort and appreciates the work he did for him during the three months he was with the campaign. He likes General Flynn personally, but understands that they have their own path with the special counsel," Cobb said.

"I think he would be sad for them, as a friend and a former colleague, if the process results in punishment or indictments. But to the extent that that happens, that's beyond his control."

Mueller is investigating whether Manafort violated federal tax laws or lobbied on behalf of foreign officials without registering. His team is also investigating Manafort for possible money laundering. Many of the activities Mueller is scrutinising date back years, well before Manafort joined the Trump campaign.

"Mr Manafort has said from the beginning neither he nor anyone else in the Trump campaign colluded with the Russian government to undermine the 2016 election," said Jason Maloni, a spokesman for Manafort.

"Finally, everyone seems to be coming to that same conclusion."

Mueller is also examining Flynn's financial ties to Russia and whether he concealed lobbying he did last year for Turkey.

The White House has given Mueller's team documents related to Manafort and Flynn, as well as the firing of FBI director James Comey and other topics. Trump has instructed all White House staff to cooperate with investigators, Cobb said.

Mueller has begun interviewing the staff, but he has not yet asked to speak with Trump.

"We'd have to address that in the future if they see a need to talk to him," Cobb said.

Cobb said none of the White House documents turned over to Mueller showed evidence that anyone colluded with Russia, or that Trump tried to obstruct justice. The President is fully cooperating with the special counsel, he said.

"I think the path that he chose of trying to minimise conflict and maximise cooperation is one that benefits the country as he tries to erase this cloud," Cobb said. "Which I think he will ultimately achieve."

He did not say when he believed that would happen, but he predicted the end of the investigation was nearing.

"I don't think that it's far away," he said.