Facebook Inc Chief Executive Mark Zuckerberg on Tuesday announced a big management shakeup, giving more responsibility to his chief product officer and launching a blockchain division.

The shakeup includes no firings or outside hires and does not change the role of either Zuckerberg or Chief Operating Officer Sheryl Sandberg.

Chris Cox, the chief product officer in charge of the flagship Facebook service, will now also oversee the widely used services Instagram, Messenger and WhatsApp, the company said.

Two other executives, Chief Technology Officer Mike Schroepfer and Vice President of Growth Javier Olivan, will oversee other consolidated divisions, one related to "new platforms and infrastructure" and another for centralized services such as the ads system.

Facebook dod not probide the reasons behind the shakeup.

David Marcus, the head of Messenger for the past four years, is leaving that role to set up a group to explore how to use blockchain technology across Facebook.

Blockchain, the technology that underpins cryptocurrencies such as bitcoin, could have other business applications as a ledger for recording transactions, although Marcus said Facebook was "starting from scratch."

Stan Chudnovsky, who has been Messenger's product chief, will succeed Marcus as head of the service, Facebook said.

Chris Daniels, who has been in charge of a Facebook effort to expand internet access, will be the head of WhatsApp, succeeding Jan Koum, the WhatsApp co-founder who said last week he was leaving the company.

Kevin Weil, head of product at Instagram, is leaving that job to join Facebook's blockchain division, and Adam Mosseri, head of the Facebook News Feed, will succeed Weil at Instagram, the company said.