An alleged hack into computer systems at the Democratic Congressional Campaign Committee has apparently exposed some embarrassing emails that show how neutral DNC officials maneuvered in favour of Hillary Clinton over Bernie Sanders as the presidential nominee.
The probe into the hack has now been taken over by the Federal Bureau of Investigation (FBI).
A Democratic aide says House Democratic leadership has been informed of the investigation. The aide demanded anonymity to discuss an ongoing investigation.
Details weren't immediately clear. The Democratic Congressional Campaign Committee is the campaign arm for House Democrats.
Cybersecurity experts who studied the hack at the DNC have blamed Russia. That hack exposed embarrassing emails indicating supposedly neutral DNC officials maneuvered in favour of Hillary Clinton over Bernie Sanders.
That resulted in party chairwoman Rep. Debbie Wasserman Schultz announcing her resignation just as the Democratic National Convention was getting under way in Philadelphia.
The DCCC hack investigation was first reported by Reuters.
(With inputs from AP)