Image copyright Reuters Image caption Elon Musk has said AI is humanity's biggest threat

Technology billionaire Elon Musk has quit the board of the research group he co-founded to look into the ethics of artificial intelligence.

In a blog post, OpenAI said the decision had been taken to avoid any conflict of interest as Mr Musk's electric car company, Tesla, became "more focused on AI".

He has been one of AI's most vocal critics, stressing the potential harms.

Mr Musk will continue to donate to and advise the group.

In 2014, Mr Musk said AI was humanity's biggest existential threat.

And in 2017, he said that the United Nations needed to act to prevent a killer robot arms race.

He founded OpenAI in December 2015, as a non-profit company working for "safer" AI.

OpenAI recently contributed to the Malicious Use of Artificial Intelligence report, which warned AI was ripe for exploitation by rogue states, criminals and terrorists.

In the blog post, OpenAI said in the coming months it would lay out the issues and policies needed to ensure that AI "benefits all of humanity".

It also announced some new donors, including video game developer Gabe Newell and Skype founder Jaan Tallin.