The US Department of Justice's investigation into Facebook's Cambridge Analytica scandal is now looking at Facebook itself, not just the defunct data firm that gained access to its user data, according to a report from The Washington Post.

Additionally, the Securities and Exchange Commission and the Federal Trade Commission have joined the Justice Department and the FBI in the inquiry, according to the report. Among other things, the investigation is scrutinizing Facebook's public statements related to the scandal, The Post reported.

"We are cooperating with officials in the US, UK, and beyond," a Facebook spokesperson said in a statement to Business Insider. "We’ve provided public testimony, answered questions, and pledged to continue our assistance as their work continues."

Facebook's stock dropped more than 1% in after-hours trading following the news, which came after the close of regular market trading.