The Kings Of Leon have fired off a letter of complaint after a British airport security worker allegedly hurled a racist slur at a member of their entourage, according to a U.K. report.

The Sex on Fire hitmakers were said to be furious after a female staff member for security firm G4S passed comment about their bodyguard as the band flew from a private terminal at Manchester Airport in England following its concert in the city on Tuesday (25Jun13).

The rockers' management team has confirmed that an official complaint letter has been sent to G4S chiefs.

A source tells Britain's The Sun on Sunday, "Apparently they came through (the airport) on Tuesday night and the woman asked who the 'big black guy' was - because he 'looks like a gorilla'. He was their security guard and the band kicked off big style."

According to a G4S spokesperson, a probe has been launched to investigate the incident.