Hilary Duff accused of lip-syncing new single on <i>X Factor</i>: 'At least match the lips to the backing track'

US pop star Hilary Duff has been called out for allegedly lip-syncing during her performance on X Factor Australia last night.

Debuting her first single in seven years, 'All About You', the former Lizzie McGuire star sparked talk on social media with claims she was miming while busting out overly complicated line-dancing moves.

It didn't help thatX Factor judge Redfoo was caught on camera looking particularly baffled by Hilary. Watch above and see for yourself.

"Watching Hilary Duff lip-sync while trying to dance was one of the most awkward things I've ever watched," wrote one fan on Twitter.

"Oh Hilary Duff! Babe, If you're going to lip-sync on X Factor. Please make it believable. At least match the lips to the backing track. Eeek," another added.

The 26-year-old's fans leapt to her defence on X Factor's Facebook page, with one writing: "Watch any audience video on Instagram of Hilary performing and you'll see that she was definitely singing LIVE."

Fans pointed out that both Hilary and the other guest US pop star for the night, Ariana Grande, were both using backing tracks. However, Ariana's voice could clearly be heard during her performances of her three hits 'Problem', 'Break Free' and 'Bang Bang'.

Hilary and Ariana are currently in Sydney on separate promo trips.

View slideshow: Worst lip-syncing fails!