Federal prosecutors are investigating campaign contributions to Virginia Gov. Terry McAuliffe (D), and what they consider suspicious personal finances, as part of a public integrity probe that has lasted for more than a year, according to two officials familiar with the inquiry.

Justice Department officials would not confirm or deny the investigation. Many details, including what prompted it, remain unclear, and one official said there is skepticism among prosecutors about whether it will lead to charges.

That official said investigators have been scrutinizing McAuliffe’s finances — including personal bank records, tax returns and public disclosure forms that date back many years — and are interested in foreign sources of income.

The officials spoke on the condition of anonymity because the investigation is ongoing and those who discuss it might face discipline. CNN first reported the probe and said investigators were interested in a contribution to McAuliffe from a Chinese businessman, Wang Wenliang, through his U.S. businesses.

Federal prosecutors have been investigating donations to his gubernatorial campaign, officials familiar with the matter said. (WUSA9)

A McAuliffe spokesman referred questions to a lawyer, Marc Elias, who said in a statement: “We cannot confirm the CNN report. Neither the Governor nor his former campaign has knowledge of this matter, but as reported, contributions to the campaign from Mr. Wang were completely lawful. The Governor will certainly cooperate with the government if he is contacted about it.”

McAuliffe — a longtime ally of Bill and Hillary Clinton and a prolific fundraiser — worked as an unpaid director for the Clinton Foundation until he was elected governor. The official said the inquiry includes McAuliffe’s time on the board. Neither the Clinton Foundation nor leading Democratic presidential candidate Hillary Clinton is a target of the probe.

Wang is a donor to both McAuliffe and the foundation. West Legend Co., the New Jersey affiliate of Rilin Enterprises, a Chinese firm led by Wang, gave $120,000 to McAuliffe’s 2013 campaign and inauguration. His $2 million pledge to the foundation drew attention last year, first from CBS News and then other outlets, because of his connections to the Chinese government — both as a member of the National People’s Congress and as a contractor entrusted to build China’s embassies.

Wang’s companies ship soybeans through Virginia ports.

Wang’s spokesman said Wang remains a Chinese citizen but lives in the United States legally. He said Wang’s contribution was legal and properly disclosed. Campaign finance records show the contributions from West Legend.

Foreign nationals are prohibited under federal law from making political contributions, except immigrants who hold green cards.

A U.S. subsidiary of a foreign corporation cannot contribute campaign funds if it is financed in any way by its parent company or if individual foreign nationals are involved in the decision to make the donation. But Wang holds U.S. permanent resident status, which makes him eligible to donate to McAuliffe’s campaign.

Clinton is separately wrestling with an investigation into her use of a private email server while she was secretary of state — which critics say could have allowed classified information to fall into the wrong hands. People familiar with that case have said it seems unlikely — at least at this juncture — to produce criminal charges, though FBI agents are still investigating and hope to interview Clinton in the coming weeks.

The McAuliffe probe is being conducted at least in part by the U.S. Attorney’s Office in the Eastern District of Virginia, which in 2014 won a conviction against former Virginia governor Robert McDonnell and his wife, Maureen, on public corruption charges. That case, though, has made its way to the Supreme Court, where justices seemed concerned that upholding the conviction could criminalize everyday interactions between politicians and campaign contributors or supporters.

McAuliffe is a wealthy man — he earned $9.5 million and paid $2.7 million in taxes in 2012, according to a summary of his tax returns released by his gubernatorial campaign. He has dabbled in a variety of business ventures that were sometimes controversial. Federal investigators, for example, probed whether a company he founded known as GreenTech Automotive received preferential treatment from U.S. government officials. McAuliffe resigned as chairman of the company in 2012.

Laura Vozzella, Matea Gold, Sari Horwitz and Anu Narayanswamy contributed to this report.