U2 have postponed the relaunch of their U2 360 tour, after lead singer Bono injured himself while preparing for the opening night.
Bono, real name Paul Hewson, has had emergency spinal surgery at a specialist neurosurgery clinic in Munich and is expected to stay there for a number of days. He will then return to his home in Ireland to recuperate further, a spokesman said.
It is not clear how the singer came to suffer the injury. Details regarding the accident have not been made available. Rehearsals for the new tour were to begin on Tuesday for the opening date in Salt Lake City, which they have already been forced to postpone.
The Irish rock band was due to perform a series of gigs across North America, returning to Europe in August. A statement on the band's website said further information about other tour dates would be announced in due course, once the singer's condition had been assessed.
U2 manager Paul McGuinness said: "We will make plans to reinstate the dates as soon as possible." He added it was "unfortunate that we're inconveniencing fans" and that it was also causing disruption to the band's 400-strong crew.
On 25 June, U2 were due to headline the Glastonbury Festival, celebrating its 40th birthday this year. That date is now in doubt. Before then a further six concerts throughout the US and Canada are scheduled, at which Lenny Kravitz is due to support. Mr McGuinness advised fans to continue monitoring the U2 website for further news. He also said the band had been planning to play some new material.
Last year Bono said the band were "delighted and humbled" at the prospect of headlining Glastonbury. When asked about preparations, he answered: "We'll certainly be well-rehearsed, we'll be coming straight from the tour."
After North America, the tour is scheduled to travel to Italy, Russia, Finland, Turkey and elsewhere in Europe. The details may now be significantly different. Last year, the 360 Degree tour, with its pioneering claw-like stage that leaves the band visible to the audience from every angle, earned them around $109m (£75.3m), making U2 the world's most profitable band of the year, according to figures from Billboard magazine. The publication also predicted it would end up being the highest-grossing tour in history, ahead of The Rolling Stone's two-year Bigger Bang tour in 2005 to 2007, which pulled in $558m (£385m).
At some concerts during last year's European leg of the tour, a video link-up with the crew of the International Space Station was aired.