Facebook is working with special counsel Robert Mueller as he investigates Russian election meddling and any ties to the Trump campaign, Facebook co-founder and CEO Mark Zuckerberg said in testimony before a joint Senate panel Tuesday.

Zuckerberg, who is on Capitol Hill this week testifying about the data sharing scandal involving data firm Cambridge Analytica, was uncertain about the existence of subpoenas from Mueller's office. But he confirmed to members of the Senate Judiciary Committee and Senate Commerce, Science and Transportation Committee Tuesday that the social media giant he founded is indeed cooperating with Mueller.

The comments came in response to questions from Sen. Patrick Leahy, a top Democrat on the Senate Judiciary Committee.

Zuckerberg first confirmed Facebook has been served subpoenas from the special counsel's office, then later backtracked on that answer and said there "may be" a subpoena, but he does know his company is working with Mueller's team.

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Asked if anyone, himself included, had been contacted by Mueller's office, Zuckerberg again said, "yes." Zuckerberg said he himself has not been interviewed by investigators, but he believes others have been.

"I want to be careful because our work with the special counsel is confidential and I want to make sure in an open session I'm not releasing something that's confidential," Zuckerberg said, treading lightly on how to answer Leahy's line of questioning.

Facebook played a prominent role in Mueller's February indictment of 13 Russians accused of interference surrounding the 2016 presidential election. The Russians are accused of using fake accounts, including on Facebook, to manipulate opinions.

This is a developing story and will be updated.

CBS News' Emily Tillett contributed to this report.