Debbie Wasserman Schultz says she is stepping down as Democratic Party chairwoman at the end of this week's convention.

The Florida congresswoman has been under fire following the publication of leaked internal emails by Wikileaks suggesting the Democratic National Committee favoured Hillary Clinton in the presidential primaries.

That prompted runner-up Bernie Sanders on Sunday to call for Wasserman Schultz's immediate resignation.

Donna Brazile, the DNC's vice chair for civic engagement and voter participation, will act as interim chairwoman.

In a statement, Wasserman Schultz says she still plans to fulfil her duties formally opening and closing the convention in Philadelphia. She also says she will speak at the four-day gathering.

In a statement Sunday, Clinton thanked Wasserman Schultz, saying she would serve as a surrogate for the Clinton campaign and as honourary chairwoman of a 50-state program to build the party in every part of the country.

"As president, I will need fighters like Debbie in Congress who are ready on day one to get to work for the American people," Clinton said.

Sanders said the resignation was the "right decision for the future of the Democratic Party," and he hoped new leadership would "open the doors of the party and welcome in working people and young people."

He also said "party leadership must always remain impartial," which he added was not the case in the 2016 Democratic primary race.

The party leadership must always remain impartial in the presidential nominating process, something which did not occur in the 2016 race. —@BernieSanders

Also on Sunday, Clinton's campaign manager accused Russia of leaking emails on purpose to help Trump in the presidential election.

Robby Mook said on CNN's State of the Union that experts are telling the campaign "Russian state actors" broke into the DNC's emails, and other experts say these Russians are now selectively releasing the emails.

He says it's no coincidence the emails are coming out on the eve of the party's nominating convention in Philadelphia