SAN FRANCISCO (REUTERS) - The co-founder of WhatsApp, a messaging service owned by Facebook Inc with more than 1 billion daily users, said on Monday (April 30) he was leaving the company, in a loss of one of the strongest advocates for privacy inside Facebook.

Jan Koum's plan to exit comes after clashing with the parent company over WhatsApp's strategy and Facebook's attempts to use its personal data and weaken its encryption, the Washington Post earlier reported, citing people familiar with the internal discussions.

"It's been almost a decade since Brian and I started WhatsApp, and it's been an amazing journey with some of the best people," Koum, WhatsApp's chief executive, said in a post on his Facebook page referring to co-founder Brian Acton.

"But it is time for me to move on."

He did not give a date for his departure and could not immediately be reached for comment.

Acton left the messaging service company in September to start a foundation, after spending eight years with WhatsApp.

Stanford alumnus Acton and Ukrainian immigrant Koum co-founded WhatsApp in 2009. Facebook bought WhatsApp in 2014 for US$19 billion (S$25 billion) in cash and stock.

WhatsApp, a pun on the phrase "What's up?," grew in popularity in part because its messages are stored on users'smartphones and not on the company's servers, making the service more private and difficult to hack.

Concerns about Facebook's handling of personal information have grown since the social network's admission in March that the data of millions of users was wrongly harvested by political consultancy Cambridge Analytica.

Facebook has taken steps in recent months to generate revenue from WhatsApp, which unlike Facebook's flagship social network does not have advertising. Koum and Facebook Chief Executive Mark Zuckerberg ruled out advertising on WhatsApp.