Britney Spears is facing embarrassment over sales of her new album.

According to early figures, Britney Jean, the singer's eighth studio album shifted just 6,400 copies on its first day of release, including pre-orders. The record, which features her single "Work B*tch," is currently at number 14 in the UK Album Chart and was released on Monday after being streamed on iTunes for a week for fans.

Critics have described the songs as "disappointing," but the 32-year-old singer said she is proud of the effort. In an open letter on her website, she said, "I poured my heart and soul into this album. I know I keep telling you it is my most personal record yet, but it's true and I'm really proud of that. I have been through a lot in the past few years and it has really inspired me to dig deeper and write songs that I think everyone can relate to."

The pop star, who will start her Las Vegas residency at Planet Hollywood this month, sold more than 30 million copies worldwide of her debut record Baby One More Time, making it one of the best-selling albums of all time.