Paid subscribers to Apple Music have soared to 20 million but the U.S. technology giant has a long way to go before it can catch the industry leader.

Apple Music added three million users to the 17 million it reported in September, Apple revealed in interviews with the BBC and Billboard.

In comparison, Spotify has 40 million paid subscribers, as of its last official statement in September. But the streaming service also has a free tier which puts its total user base at 100 million.

Apple Music launched 18 months ago and since then has been growing steadily. It has been aggressive in securing exclusive deals with artists, a move that it has come under fire for. Apple Music boss Eddie Cue told the BBC that it had hosted 70 exclusives over the last year, such as rapper Drake's "Views" album.

But the industry has hit back at the tactic. Universal Music Group has stepped back from offering exclusive deals to streaming services and earlier this year, rapper Kanye West went on an expletive-filled rant suggesting that the battles between Apple and other streaming players is ruining the music business.

Cue said that exclusives will continue in the future.

They work really well for everybody concerned – they're great for the label, they work for the artist and for us," Cue told Billboard in an interview.

Services such as Apple Music have become increasingly important for the company as it looks to grow new areas of the business amid a recent slowdown in iPhone sales. Revenue from services which includes Apple Music and Apple Pay, rose 24 percent year-on-year in the company's recent fiscal fourth quarter.

Despite still trailing Spotify in terms of size, Cue said there is still a lot of room to grow.

"We can't forget that, as an industry, we still have very few music subscribers. There are billions of people listening to music and we haven't even hit 100 million subscribers. There's a lot of growth opportunity," Cue said in the Billboard interview.