Keane frontman Tom Chaplin is being treated for drink and drug problems, the band have confirmed.
Keane performed at the V Festival over the weekend
In a statement on the band's website, the 27-year-old said the time had come "to get the professional help I need to sort myself out".
Earlier this month the band cancelled shows in Edinburgh, Dublin and Ibiza, saying at the time that the singer was suffering from exhaustion.
They have also postponed a North American tour planned for next month.
Chaplin's statement said: "I've been having to deal with an increasing problem with drink and drugs, and the time has come to get the professional help I need to sort myself out.
"I feel desperately disappointed to be letting down our fans, but I want to get myself right now so that I can be back on the road for the rest of the year."
The band, who played at last weekend's V Festival, said refunds for cancelled concerts should be sought at the point of purchase.
Keane, who also feature drummer Richard Hughes and keyboard player Tim Rice-Oxley, won two Brit Awards last year for best British album, for their debut Hopes and Fears, and best British breakthrough act.
Two years ago, they topped the BBC News website's Sound of 2004 poll of UK critics and broadcasters, which focuses on up-and-coming acts.
Their follow-up album, Under the Iron Sea, entered the UK chart at number one in June.