Black Sabbath have cancelled their scheduled European tour this summer, revealing that their sole performance as a band will be at the UK's Download Festival.

The news comes off the back of last month's revelation that guitarist Tony Iommi had been diagnosed with lymphoma.

The British metal act had announced in November last year that they were reforming their original lineup to record their first album together in more than 33 years as well as performing a worldwide tour.

In order to try and salvage something from the tour, frontman Ozzy Osbourne will play the rest of the slated European shows with a host of guest musicans in what is being billed as Ozzy & Friends.

An official statement added that musicians slated to appear alongside Osbourne include former Guns N' Roses guitarist Axl Rose, Black Sabbath bassist Geezer Butler, and former guitarist with the Prince of Darkness' solo act, Zakk Wylde.

Black Sabbath's reunion plans have been further hampered by an ongoing dispute with the band's drummer Bill Ward. Earlier this month, in an open letter, Ward said he would not proceed with the band until he received a contract that he felt treated him with due respect.

In a statment on his website today, though, Ward claims that he is anxious to continue work with the band.

At the earliest opportunity, I am prepared to go to the UK and record, and later tour with the band.

Last week, we sent further communication to the attorney handling the negotiations to try to reach an agreement. At this time we are waiting to hear back. I remain hopeful for a 'signable' contract and a positive outcome.

With so much uncertainty and drama now hanging over the reunion, fans once high expectations for the album and tour are certain to be decreasing by the day.