Tech giant Google has fired the head of its artificial intelligence (AI) ethics programme, claiming she had broken the rules on moving files outside of the company.

Margaret Mitchell tweeted the she had been let go by the firm on Friday, with the move coming a month after she had publicly vented about the way her former peer, Timnit Gebru, was dismissed.

In a statement, Google said that Ms Mitchell's violations "included the exfiltration of confidential business-sensitive documents and private data of other employees" following an investigation last month.

According to some reports, Ms Mitchell had been locked out of her work account for five weeks in the build up to her dismissal, including her emails and the corporate system.

Her colleague, Ms Gebru, left Google late last year and says she was fired - but the firm said she resigned - in a dispute over a research paper.

Ms Mitchell and Ms Gebru, who co-led the firm's ethical AI team, had campaigned for wider diversity at Google, and had previously raised concerns about the censorship within the company.

Ms Gebru gained prominence after exposing bias in facial recognition systems, and had apparently been asked not to publish a study that claimed that AI could hurt marginalised groups.

Ms Mitchell was a co-author of the paper and said that by dismissing her colleague, Google had undermined the credibility of her work.

Ms Mitchell has been a frequent critic of Google's handling of the dismissal of her former colleague, saying the firm has a problem with sexism and discrimination.

Alex Hanna, another Google employee, claimed on Twitter that the firm was running a "smear campaign" against the two women, with whom she had previously worked with. Google declined to comment on Dr Hanna's claims.

Staff were told of Ms Mitchell's dismissal on Friday morning in a meeting by Google's AI research director Zoubin Ghahramani and a company lawyer.

A source told news agency Reuters that little explanation was given for the firing. Google has not commented on the claims.