Democratic presidential candidate Clinton speaks during the "Women for Hillary" endorsement event and fundraiser Thomson Reuters The FBI is widening its investigation of Democratic presidential candidate Hillary Clinton's use of a private email account while she was U.S. secretary of state to determine whether any public corruption laws were violated, Fox News reported on Monday.

The Federal Bureau of Investigation has been looking into whether classified material was mishandled during Clinton's tenure at the State Department from 2009-2013.

It will expand its probe by examining possible overlap of the Clinton Foundation charity with State Department business, Fox reported, citing three unidentified intelligence officials.

"The [FBI] agents are investigating the possible intersection of Clinton Foundation donations, the dispensation of State Department contracts and whether regular processes were followed," Fox quoted one of its unidentified sources as saying.

The FBI and the State Department had no immediate comment on the report. The Clinton campaign didn't immediately respond to a request for comment from Business Insider.

Republican National Committee Chairman Reince Priebus issued a statement calling the Fox News report "a very troubling development."

The FBI last expanded its probe into the server in November to examine whether "materially false statements" were ever provided to agents throughout the course of the case.

U.S. Democratic Presidential candidate Hillary Clinton speaks at a campaign stop in Reno, Nevada Thomson Reuters Facing criticism last year for exclusively using a private server during her time as US secretary of state, Clinton handed over about 30,000 work-related emails for the State Department to make public. She deleted about 31,000 more emails she says were personal in nature.

The FBI launched its investigation into Clinton's server in August in an effort to determine whether any classified information ever passed onto the server while she served as secretary of state.

After months of negative headlines that battered her campaign, the Democratic presidential front-runner apologized in September for her email arrangement. But she has insisted that she didn't violate protocol — noting that she used communication practices that were widespread across the federal government — or pass along material marked classified.

More than 1,200 emails in Clinton's server have been retroactively marked "classified" since the investigation began in August, according to Politico.