"I've sustained a vocal injury and been told I cannot sing for a week... seriously I felt something snap, it was very frightening," wrote Welch, 25, to her fans on the band's website (www.florenceandthemachine.net).

"Unfortunately this means I will not be able to perform at the Benicassim and Optimus Alive festivals (in Spain and Portugal respectively) this weekend... I hope I can make it up to you in the future."

She did not specify the nature of the vocal injury, "but I was told without question not to (perform), so as not to do permanent damage."

Florence and the Machine is still lined up for a string of concerts in Canada and the United States starting in Burnaby, British Columbia on July 20 and ending in Chicago on August 5, before returning to Europe for more gigs.

Fellow British songstress Adele canceled a number of US concerts in October last year after she sustained a vocal cord hemorrhage for the second time in less than a year. In such cases, doctors prescribe strict voice rest.