Britney Spears was injured while dancing on-stage in Illinois

The 22-year-old was injured during a dance routine as she performed the song Boom Boom as an encore at Moline.

She cut short the performance and reappared on stage a few minutes later to apologise to the audience.

Spears has called off dates in Chicago and Detroit, according to her record company, Jive. She is expected to resume the tour in Atlanta on Tuesday.

The cancelled dates are expected to be rescheduled for April, said a spokeswoman.

Scheduled

Spears is currently in the middle of her Onyx Hotel Tour, with dates also scheduled for Europe and Asia. She is promoting her fourth album In The Zone, which was released last November.

The singer recently celebrated a Number One single in the UK with Toxic - her first chart-topper in the country for around four years.

The single's global success marked a revival in fortunes for the singer, whose album received a mixed reaction from the critics.