HOLLYWOOD, Calif. — Britney Spears is ripped and ready to go!

The 27-year-old pop star's tight body was on display Friday in new photos posted on her Web site. The pictures come from Spears' rehearsal session on Monday night as she prepares for her upcoming "Circus" concert tour.

Spears, shown wearing Lisa Kline J'aime Drawsting Pants, is captured working with contributing choreographers JaQuel Knight and Jose (the "Womanizer" from her recent European performances) in the rehearsal gallery.

Spears has shed a reported 20 pounds in recent months by cutting her diet to 1,200 calories per day. That's in addition to a rigid cardio-and-strength-training program, on top of her dance rehearsals.

"I have had to work hard at getting [my body] back to where it used to be," she revealed in January's Glamour. "I used to be obsessed with working out ... But I can't get motivated right now because I'm so focused on my music."

Spears kicks off her world tour on March 3 in New Orleans, along with special guests The Pussycat Dolls.

Buy tickets for the Britney Spears "Circus Tour"