WASHINGTON • US President Donald Trump said he fired Paul Manafort as his campaign chairman to avoid "potential conflicts" with "certain nations", according to excerpts of an interview.

Manafort and his associate Richard Gates were placed under house arrest last week on money laundering charges linked to a probe by special counsel Robert Mueller.

The charges relate to allegations that the then Republican presidential candidate's campaign colluded with Russia in the run-up to the November 2016 election.

The United States Congress is also conducting three separate investigations into the allegations, which have dogged Mr Trump since his election and which he has strongly denied.

Asked who recommended Manafort to manage the campaign, Mr Trump said last Saturday that "it was a friend of mine who was a businessman - a very successful businessman and a good person, and you know, Paul was not there very long".

"I think we found out something about (how) he may be involved with all - with certain nations, and I don't even know exactly what it was in particular," he told Sharyl Attkison's syndicated television show Full Measure.

"But there was a point at which we just felt Paul would be better off - because we don't want to have many potential conflicts," he added.

Mr Trump also said he has no current plans to fire Mr Mueller.

"Well, I hope he's treating everything fairly, and if he is, I'm going to be very happy, because when you talk about innocent, I am truly not involved in any form of collusion with Russia," he added.

Manafort and Gates have pleaded not guilty to charges that they hid millions of dollars gained from work with Ukrainian politician Viktor Yanukovych and his pro-Moscow political party.

In the Saturday court filing, Manafort offered to limit his travel to New York, Washington and Florida, and pledged life insurance worth about US$4.5 million (S$6.1 million) and about US$8 million in real estate assets, including a property on Fifth Avenue in New York identified by some media outlets as an apartment in Trump Tower.

AGENCE FRANCE-PRESSE, REUTERS