Bono has revealed that he thinks U2 are "on the verge of irrelevance".

The frontman said in an interview with BBC Radio 1's Zane Lowe that the band are still working on their upcoming 13th studio album, after releasing their latest song Invisible as a free download after the Super Bowl on Sunday (February 2).

When asked if it was difficult to stay relevant, Bono said: "We're on the verge of irrelevance. You have to make stuff relevant to you and where you're at, make an honest account of what you're going through. If that's relevant to other people, great. But we don't know."

The singer added that U2 should have the new record ready in two month's time, explaining: "We're here in this great nation, in this capital, in some dank basement where there were mice earlier. We call it the oil rig."

He also opened up on the inspiration on the album, saying: "We went back to why we wanted to be in a band in the first place... We were listening to The Ramones and Kraftwerk - you can hear both on Invisible. It opened up a whole valve for me writing, it was like a dam-burst of sorts."

The band raised over €1.5m for charity by donating the proceeds from the sales of Invisible to help the fight against Aids.

U2 made the new song available as a free download for 24 hours with the Bank of America giving Bono's charity Red $1, or 73c, a download.