U2 are playing stadium gigs in America as part of the Vertigo tour

The band were angered after Democrat Ms Clinton gave supporters a chance to be in her suite at the band's Washington concert in return for a party donation.

Republican senator Rick Santorum is making a similar offer for U2's Philadelphia show.

"U2 concerts are categorically not fundraisers for any politician," said a band spokesman.

He added: "They are rock concerts for U2 fans."

Political offers

New York senator Ms Clinton is offering the chance for 18 people to join her in a luxury suite at Washington's MCI Center when U2 play the venue on 19 October.

Supporters have to contribute $2,500 (£1,430) to the Democratic Party to get a place.

The former first lady's spokeswoman said: "We do a meet-and-greet with the senator, and then go in and listen to music."

Pennsylvania senator Mr Santorum is holding a similar event at the Philadelphia show this Sunday with places costing $1,000 (£572) per person.