French prosecutors have begun an inquiry of US tech giant Apple over suspected "planned obsolescence" in some of its iPhone models, a judicial source has said.

The investigation was opened on Friday and is being led by competition and consumer protection specialists in the French economy ministry.

It comes after a complaint by the association Stop Planned Obsolescence after Apple admitted last month that it intentionally slowed down older models of its iPhones over time.

Planned obsolescence is a widely criticised commercial practice in which manufacturers build in the expiry of their products so consumers will be forced to replace them.

It is decried by consumer groups as being unethical and is suspected of being particularly prevalent in the electronics industry, which produces mountains of unrecyclable waste each year.

To tackle the problem, France passed landmark legislation in 2015 known as "Hamon's law", which made the practice illegal and in theory obliged retailers to say whether replacement parts were available.

The law stipulates that a company found to be deliberately shortening the life of its products can be fined up to 5% of its annual sales while executives can face up to two years in jail.