Democratic presidential frontrunner Hillary Clinton is facing additional scrutiny over as much as $26 million payments the Clinton Foundation received for speeches given by the former first lady, her husband, former President Bill Clinton, and the couple's daughter, Chelsea Clinton, the New York Daily News reported.

The payments had not been previously disclosed and raised concerns over whether the organization fully complied with a 2008 promise to reveal all its donors so they could be publicly vetted for possible conflicts of interest. Following Barack Obama's White House win, Clinton was picked that year to lead the Department of State, a post she held through the end of the president's first term in office.

The payments in question came from major corporations and universities, both in the United States and abroad, the New York Daily News detailed.

The Clinton Foundation reported them in ranges rather than exact amounts, making it impossible to calculate the precise total the Clintons earned for the charitable foundation, the newspaper added.

The funds were tallied internally as "revenue," rather than donations, which is why they had not been included in the public listings of its contributors published as part of the 2008 agreement, foundation officials told the Washington Post. According to the new information, Bill, Hillary and Chelsea Clinton have delivered 97 speeches to benefit the charity since 2002, of which more than two dozen were sponsored by colleges and universities, the newspaper added.

Foreign contributions to the Clinton Foundation had already proved to be a headache for the Democratic White House contender earlier this year. In February, for example, the Hill revealed that the Clintons' nonprofit received hundreds of thousands of dollars from a Canadian government agency.

The Wall Street Journal, meanwhile, had pointed to an uptick in contributions from foreign governments that coincided with Hillary Clinton's moves toward her 2016 White House bid: In 2013, Australia, Italy, the Netherlands and Norway all chipped in, and the number of governments that donated in 2014 appeared to have doubled from the previous year, the newspaper detailed.