Britney Spears' manager has spoken out to defend the pop star over accusations she mimes during her Las Vegas residency, insisting it is "virtually impossible" for her to sing throughout the show.

The Toxic hitmaker ended her first run of concerts at the Planet Hollywood Hotel & Casino resort last month (May14) and she is due to return in August (14) for another 50 gigs.

Her initial residency in Sin City attracted criticism that she was not singing live at various points during the performance, and now her manager Adam Leber has defended the pop star.

He tells Medium.com, "To put on the show that she puts on, it's virtually impossible to sing the entire time and do what she does. She's singing on every song, basically, when she has the ability to sing. There's no way you can dance for 90 minutes straight and sing the entire time."