Britney Spears has revealed that she has been working with Sia on some "special" new music.

The pop princess is currently working on the follow-up to her 2011 album 'Femme Fatale', which hit No.1 in the US upon release.

Spears has now updated fans on Twitter with the news that she has been working with hitmaker Sia on some new tracks. She said:

"Had an AMAZING writing session today with the beautiful and talented @Sia. We wrote such a special song together :)."

Sia has previously penned tracks like Rihanna's 'Diamonds' and has appeared on songs such as David Guetta's smash hit 'Titanium'.

She replied to Spears' tweet: "Oh gosh miss @britneyspears is the sweetest. Very special day."

As previously reported, Britney Spears recently revealed the video for her track 'Ooh La La', which features on the soundtrack of new film The Smurfs 2.