By Joseph Menn

(Reuters) - Facebook chief information security officer Alex Stamos is leaving the company in August, a source said on Monday, and a report cited internal disagreements over how the social network should deal with its role in spreading disinformation.

The social media company has already taken away Stamos' responsibilities to counter government-sponsored disinformation, the source said.

Not denying his exit, Stamos tweeted that his role at the company did change, but he was still fully engaged with work at Facebook.

Facebook could not be immediately reached for comment.

The New York Times first reported his departure from the company.

Inside Facebook, Stamos had been strongly advocating for investigating and disclosing Russian activity on the social media platform, often to the consternation of top executives, including Chief Operating Officer Sheryl Sandberg, the newspaper said.

Stamos' responsibilities were reassigned in December after which Stamos said he would leave the company, the Times said.

Stamos was persuaded to stay through August to oversee the transition of his duties because company executives thought his exit would look bad, it said, citing current and former employees.

Facebook's reputation is already under attack over Russia's alleged use of Facebook tools to sway U.S. voters with divisive and false news posts before and after the 2016 election.

The company is under fresh scrutiny after media reports that political consultancy Cambridge Analytica harvested private information from more than 50 million Facebook users in developing techniques to support President Donald Trump's 2016 election campaign.

(Reporting by Sangameswaran S in Bengaluru and Joseph Menn in San Francisco; Editing by Richard Chang and Cynthia Osterman)