The band's sixth studio album is not due until June

Unfinished mixes of tracks from Hail To The Thief are already available for downloading by fans.

Radiohead have previously spoken in favour of using the web to obtain music, but they have said they are not responsible for any leak.

Guitarist Jonny Greenwood said he felt "bemused, though not annoyed".

"It's a little earlier than we'd expected, but there it is," he said.

Contributors to some of the band's fan websites have expressed their excitement about the songs turning up online.

Greenwood said he was pleased that the tracks were receiving such a positive reaction.

However, Radiohead producer Nigel Godrich pointed out that they were unfinished versions.

"It's the rough mixes, some tracks not even finished," he said. "Not really what I'd want the world to hear, frankly."

Most of them had been previewed at shows in Spain and Portugal last year.

The band's sixth studio album is due for release on 9 June.

It supposedly takes its name from a phrase used after George W Bush became US president following a disputed vote count.