A 35-second snippet of a previously-unreleased Kurt Cobain song has been made available, Digital Spy reports.

The track features on Brett Morgen's documentary Kurt Cobain: Montage of Heck, which is out in cinemas now.

"Once I stepped into Kurt's archive, I discovered over 200 hours of unreleased music and audio, a vast array of art projects - oil paintings, sculptures - countless hours of never-before-seen home movies, and over 4,000 pages of writings," Morgen said of the vault of material available to him.

Morgen confirmed to Digital Spy last week that the tracklisting of any CD soundtrack for Montage of Heck had not yet been confirmed.

He added: "I felt like I would have approached the film in the same way if this was a film about a guy named Bob Smith who left the same material behind.

"I felt a responsibility to [Kurt's daughter and the film's executive producer] Frances [Bean Cobain]. And to be quite honest, I figured if it passed her barometer then it would work for a larger audience."