Britney Spears has been accused of lip-syncing during the launch of her Las Vegas residency.
The pop star kicked off her Britney: Piece Of Me shows at the Planet Hollywood Resort and Casino on Friday, and concert reviewers have now accused the star of miming.
The singer's manager, Larry Rudolph, had previously insisted the show would not be mimed, saying, "There might be some numbers where she's full out dancing with a (vocal) track underneath her, but there won't be any lip-syncing across the board."
Caryn Ganz of Rolling Stone is adamant Spears was not singing live.
"While the show's producers claim Spears is singing along with backing tracks of her own voice, there was little evidence Britney sang a live note," Ganz wrote.
Mikael Wood of The Los Angeles Times wrote: "The singer's presence felt so diminished - her dancing a tentative shadow of what it used to be, her vocals apparently lip-synced for the majority of the show."
Keith Caulfield of Billboard.com wrote: "The vast majority of the show was lip-synced, and only occasionally were any seemingly live vocals heard.
"There was a certain thrill in actually hearing Spears breathing into the microphone - however infrequent."
However, USA Today's Marco della Cava could not decide whether the star was singing or not.
"As for the oft-raised spectre of lip-syncing, it's impossible to gauge whether there was any funny business with the vocals..." he wrote.
"These club-oriented tunes all require such different effects that her voice surely had to be run through computers to correspond with the tone of what was recorded in the studio."
In 2011 Spears was accused of miming during shows on her Femme Fatale Tour.