Hilary Duff's camp is hitting back at reports that the actress and singer was caught lip-synching during a concert stop in Mexico this past weekend.

"She was not lip-synching," her reps tell PEOPLE. "It was faulty equipment. There was no sound coming out, but she was singing."

In a clip of the concert, Duff is seen bending over the mic and singing into it, but her voice can't be heard.

According to the reps, who have spoken to Duff and members of her tour staff about the incident, the alleged gaff was far from an Ashlee Simpson moment. Duff was relying on local sound equipment rather than her regular gear, and her microphone was inadvertently set to mute for the first few seconds of her performance. (In 2004, Simpson was caught lip-synching on Saturday Night Live.)

Duff reps insist that she performs live at her concerts.

The star's "Dignity" tour is scheduled to continue in Mexico before moving to Brazil and Australia in the coming weeks.