After the completion of their recent tour, Bono says the time is ripe for U2 to reinvent itself musically.

He told the BBC: "Our band has certainly reached the end of where we've been at for the last couple of albums. I want to see what else we can do with it, take it to the next level; I think that's what we've got to do.

"We're gonna continue to be a band, but maybe the rock will have to go; maybe the rock has to get a lot harder. But whatever it is, it's not gonna stay where it is. I would like to do a couple of [acoustic] tunes...with just a lot of space around the voice. I'd like to strip things down; that's something I'd be very interested in at the moment."

U2 plan to release a new album before the end of 2007.