Federal prosecutors are examining whether foreigners illegally funnelled donations to President Trump’s inaugural committee and a pro-Trump super PAC in hopes of buying influence over American policy, according to people familiar with the inquiry.

The inquiry focuses on whether people from West Asian nations — including Qatar, Saudi Arabia and the UAE — used straw donors to disguise their donations to the two funds. Federal law prohibits foreign contributions to federal campaigns, political action committees and inaugural funds.

The line of questioning underscores the growing scope of criminal inquiries that pose a threat to Trump’s presidency. The special counsel, Robert S. Mueller III, is focusing on whether anyone in the Trump campaign conspired with Russia to tip the 2016 presidential election in Trump’s favour, while prosecutors in New York are pursuing evidence he secretly authorised illegal payments of hush money to silence accusations of extramarital affairs that threatened his campaign.

The inquiry into potential foreign donations to the inaugural fund and the super PAC is yet another front being pursued by multiple teams of prosecutors. Thomas J. Barrack Jr, a billionaire financier and one of Trump’s closest friends, raised money for both funds.

“Tom has never talked with any foreign individual or entity for the purposes of raising money for or obtaining donations related to either the campaign, the inauguration or any such political activity,” said Owen Blicksilver, a spokesman for Barrack. The inaugural committee focus was reported earlier on Thursday by The Wall Street Journal.

The super PAC, Rebuilding America Now, was formed in the summer of 2016 when Trump’s presidential campaign was short of cash and out of favour with many major Republican donors. While Trump insisted that he could finance his own campaign, he refused to dig too deeply into his own pockets.

According to several of the people familiar with the investigation, Paul Manafort, who then headed the campaign, suggested that Barrack step into the void, creating and raising funds for the political action committee, which could collect unlimited amounts of money as long as it avoided coordinating closely with the candidate.

In an interview with investigators a year ago, Barrack said that Manafort seemed to view the political committee as an arm of the campaign, despite laws meant to prevent such coordination, according to a person familiar with the interview.

Federal election law requires a cooling-off period of at least 120 days before campaign staff members join a political committee backing the same candidate, but Manafort dispatched two friends from the campaign, Laurance Gay and Ken McKay, to run the operation. A press officer said at the time that the committee violated no rules because the campaign never paid the two men. Neither man returned repeated phone calls seeking comment.

According to filings with the Federal Election Commission, the committee raised $23 million, making it one of the most important sources of funds for advertisements, polls and other political expenditures on Trump’s behalf.

Most money came from several big donors, including from Linda McMahon, a professional wrestling executive who donated $6 million. Prosecutors from New York and from Mueller’s team have asked witnesses whether anyone from Qatar or other West Asian countries also contributed money, perhaps using American intermediaries.