A top Google scientist on ethical artificial intelligence says she was fired after criticising the company's diversity efforts, a claim the Alphabet Inc unit disputed on Thursday, in the latest brush-up between the internet giant and worker activists.

Timnit Gebru, who is black, said on Twitter she was fired on Wednesday after sending an email to colleagues expressing frustration over gender diversity within Google's AI unit and questioning whether company leaders reviewed her work more stringently than that of people from different backgrounds...