MADRID - Barcelona authorities might fine U2 for rocking too long and loudly during rehearsals for their latest world tour, the city council said Thursday.

While the city said it is proud to host the beginning of U2's world tour, it also said that one of its districts received a formal complaint by residents about the band playing after permitted hours and making noise.

"The District of Les Corts has fulfilled its duty in attending to neighbours' complaints and has acted administratively in the face of a possible failure to comply with time and noise creation regulations," the statement said.

The council said they had given the band permission to rehearse until 10 p.m., limiting the amount of sound they could make.

Regional newspaper El Punt said the band had rehearsed till midnight at sound levels measured at 70 decibels - the equivalent of a vacuum cleaner at one metre.

When called by The Associated Press, city authorities would not say how much a possible fine could add up to. But newspaper El Mundo said on its website that under current noise pollution legislation, fines of up to 15,000 euros were possible.

The Irish quartet kicked off their "360 degree" tour at Barcelona football club's Camp Nou stadium by playing 22 songs in front of 90,000 fans on Tuesday.

The show features a large, modernistic four-legged construction which houses what the band calls "a giant spherical screen."

Singer Bono told the audience after four songs, "This has been our neighbourhood for the last couple of weeks."

Some neighbours clearly were not impressed with the band's state of the art sound equipment and assiduous rehearsals.

"While business outlets cash in on fans flooding in, residents can't even open their windows at home," local businessman Alfons Huescar told journalists.