Donna Brazile, a former Democratic National Committee (DNC) interim chair, has claimed that the party organisation helped Hillary Clinton’s campaign “rig” the 2016 Democratic primary against Bernie Sanders.

In a Politico op-ed, Ms Brazile alleged that Ms Clinton was controlling the finances of the party before officially winning the 2016 Democratic nomination for president.

“This was not a criminal act, but as I saw it, it compromised the party’s integrity,” Ms Brazile said about the arrangement.

The piece, titled Inside Hillary Clinton’s Secret Takeover of the DNC, is an excerpt from Ms Brazile’s forthcoming book.

Last year, Ms Brazile took over as DNC chair after Representative Debbie Wasserman Schultz was forced out of the role over leaked emails suggesting she may have favoured Ms Clinton during the primary.

“I had promised Bernie when I took the helm of the Democratic National Committee after the convention that I would get to the bottom of whether Hillary Clinton’s team had rigged the nomination process, as a cache of emails stolen by Russian hackers and posted online had suggested,” Ms Brazile wrote.

“By Sept 7, the day I called Bernie, I had found my proof and it broke my heart,” Ms Brazile said.

The proof, according to Ms Brazile, was a joint fundraising agreement between the DNC, the Hillary Victory Fund and Hillary for America. It had been signed in August 2015, four months after the former Secretary of State announced she was running for president and a year before she officially became the Democratic nominee.

Sources point to FBI office in New York City for Hillary Clinton leaks Show all 8 1 /8 Sources point to FBI office in New York City for Hillary Clinton leaks Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÃs private email server. (Photo by Drew Angerer/Getty Images) Getty Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÕs private email server. (Photo by Drew Angerer/Getty Images) Getty Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÕs private email server. (Photo by Drew Angerer/Getty Images) Getty Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÕs private email server. (Photo by Drew Angerer/Getty Images) Getty Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÕs private email server. (Photo by Drew Angerer/Getty Images) Getty Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÃs private email server. (Photo by Drew Angerer/Getty Images) Getty Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÃs private email server. (Photo by Drew Angerer/Getty Images) Getty Sources point to FBI office in New York City for Hillary Clinton leaks NEW YORK, NY - NOVEMBER 4: A view of the Jacob K. Javits Federal Building, where the Federal Bureau of Investigation (FBI) has a field office on the 23rd floor, November 4, 2016 in New York City. FBI Director James Comey informed Congress last Friday that his agency was taking steps to review newly discovered emails relating to Democratic presidential candidate Hillary ClintonÃs private email server. (Photo by Drew Angerer/Getty Images) Getty

Ms Brazile said joint fundraising committees were created between the DNC and both the Clinton and Sanders campaigns during the 2016 election cycle. However, Ms Clinton was the only candidate who raised money for the party, she said.

In a statement to Fox News, Ms Wasserman Schultz didn’t directly address Ms Brazile’s allegations but defended her tenure as head of the DNC.

"It was a tremendous honor to be asked by President Obama to serve as chair of the DNC,” Wasserman Schultz said on Thursday. “I am proud of the work our team did to support Democrats up and down the ballot in the 2016 election and to re-elect the president in 2012.”

DNC spokesperson Xochitl Hinojosa, who works under current DNC chair Tom Perez, told Fox News that the party’s official policy is to not take sides during the primaries.

“The DNC must remain neutral in the presidential primary process, and there shouldn’t even be a perception that the DNC is interfering in that process,” Ms Hinojosa said.

In an interview with CNBC, Mr Perez said, “We’re moving forward”, when asked about the Ms Brazile’s allegations.

“One of my goals here as DNC chair is to make sure that the nominating process for 2020 is a process that is totally fair and transparent for everybody,” he said.