U2 fans are going to have to wait until next year to hear their new album because the band is going through a perfectionist phase, according to frontman Bono.

Recording is still ongoing for what will be their 12th studio album -- the follow-up to 2004's 'How To Dismantle An Atomic Bomb'. It is expected to be called 'No Line On The Horizon'.

It was originally set for a late November release but now won't see the light of day until early 2009.

The band are currently working on the album in their studio in the south of France. And they have revealed that the new record will hark back to the sound of their massive-selling 1987 LP 'The Joshua Tree'.

Bono said that he had thought the album would be finished this year, but the band have lofty ambitions for the new material.

He said: "We've hit a rich songwriting vein. It gets a bit dark down here but looks like we've found diamonds, not coal. I thought a while back we might have the album wrapped by now, but why come up above ground now if there's more priceless stuff to be found?

"This is our chance to defy gravity once again. We have what it takes, we have the songs, new rhythms and a guitar player who is not ready to re-enter earth's atmosphere until he's taken a slice off the moon.

"This one is nearly ready for the new year of 2009."

And Bono added that the new record will be a return to the band's more iconic albums.

"It's a brand new chapter for us," Bono wrote on the band's website, U2.com. "Everyone we've played the tracks to has said that musically it feels like another departure.

"The last two records were very personal, with a kind of three-piece at their heart, the primary colours of rock -- bass, guitars and drum. But what we're about now is of the same order as the transition that took us from 'The Joshua Tree' to 'Achtung Baby' (released in 1991)."

Bono added that the band won't leave the studio until they believe they have made their best ever album.

"We know we have to emerge soon but we know that people don't want another U2 album unless it is our best ever album. It has to be our most innovative, our most challenging, or what's the point?"

Following recording sessions in Morocco, Dublin and France, the band now have "50 or 60" tracks and counting.