In November, the original four man line-up announced it would record its first new album in 33 years and stage a 2012 world tour, joining the long list of ageing acts hitting the road for lucrative live performances.

But Iommi was diagnosed with cancer in January, forcing the group to move from Los Angeles to Britain in order to continue recording while he underwent treatment.

Since then, drummer Bill Ward has said he would not participate in the reunion recordings and tour unless he was offered a "signable" contract.

The setbacks mean Black Sabbath will now only perform one of their planned European dates -- Britain's Download Festival -- on June 10.

Lead singer Ozzy Osbourne will perform the remaining scheduled dates as "Ozzy & Friends," featuring himself, original Black Sabbath bassist Geezer Butler and Zakk Wylde.

Guitarist Slash will join the performers at select shows.

"Tony Iommi continues to make excellent progress and is looking forward to getting back out on the road," a statement on the band's website said. "Meanwhile, Black Sabbath continue to write and record music in the UK for their upcoming album."

There was no fresh word on Ward's involvement or otherwise.