But Tim Cook indicated that it is too soon to say whether it would license the tech to other carmakers or try to build its own vehicles.

His interview with the Bloomberg news agency yielded his most detailed comments about the project to date.

Until now, Apple had avoided publicly discussing its plans, although it had confirmed the scheme in US filings.

There had also been leaked details of a change in leadership of the car team, with veteran hardware specialist Bob Mansfield reportedly put in charge last year, as well as images of test vehicles being published on rumour sites.

"We're focusing on autonomous systems and clearly one purpose of autonomous systems is self-driving cars - there are others," Mr Cook told Bloomberg.

"And we sort of see it as the the mother of all AI [artificial intelligence] projects.

"It's probably one of the most difficult AI projects to work on.

"We'll see where it takes us. We're not saying from a product point of view where it will take us, but we are being straightforward that it's a core technology that we view as very important."

He added that the rise of AI, electric vehicles and ride-sharing presented an opportunity.

"There is a major disruption looming," he said.

"You've got kind of three vectors of change happening generally in the same timeframe."

Apple invested $1bn (£785m) in China's ride-hailing service Didi Chuxing last year.

The publication of the interview coincides with an announcement by General Motors that it has completed production of 130 self-driving Chevrolet Bolt cars at a factory in Michigan.

It intends to start testing them in San Francisco and Scottsdale, Arizona, in conjunction with the ride-hailing firm Lyft next month,

Jaguar Land Rover also revealed plans this week to test self-driving cars with Lyft in the future.

Meanwhile, Audi has begun teasing a July reveal of a new car - the A8 - that will introduce semi-autonomous features of its own.

"It's still very unclear who is going to come out on top in this space," commented Jim Holder, editorial director of Autocar magazine.

"There has been a period of about five years in which car companies and tech companies have been dancing around each other being very wary of the other's motivations.

"Now it looks like they have realised they have to get into bed together to succeed.

"Apple appears not to have an appetite to get into the carmaking business, which is famously low profit margin and high investment. But it can succeed by being a supplier and doing what it does best, which is working to seven-month cycles, while the car industry is more used to working on a seven-year cycle to produce a vehicle."