Apple has hired Google's former head of search and artificial intelligence to lead its machine learning and AI strategy.

John Giannandrea will report directly to chief executive Tim Cook, the New York Times reported on Tuesday.

The appointment comes at the same time that the tech giant looks to develop its Siri digital assistant.

It was reported last week that Apple was looking for more than 150 engineers to work on the platform.

Mr Giannandrea joined Google in 2010 after it acquired the search start-up Metaweb, where he had served as chief technology officer.

He previously worked as Netscape's chief technologist.

Analysts say that Siri, which was first introduced on the iPhone 4S in 2011, has since fallen behind offerings from competitors, such as Amazon Alexa and Google Assistant.

The company's strong stance on protecting user data, as well as its secrecy, are thought to pose a challenge to machine learning - something that Apple has denied.

"Apple keeps more user data on the device, and sends less to its servers, than Google, Amazon or Facebook," Martin Garner, senior vice president of CCS Insight, told the BBC.

"That's good for users, but it means it has less detailed data for training its AI models than the other players.

"The AI world will be very interested to hear from Mr Giannandrea how he plans to tackle this dilemma to make Apple's AI fully competitive."

In an internal memo obtained by the New York Times, Mr Cook told employees that Mr Giannandrea "shares our commitment to privacy and our thoughtful approach as we make computers smarter and even more personal".