Rihanna's US tour under threat?

Rihanna is reportedly on the brink of axing a series of US shows after poor ticket sales.

The 'S&M' singer's management team are urging her to cancel a number of Stateside concerts after poor pre-sales last month, according to the New York Post.

'It has been a big disappointment,' a source said. 'The ticket sales in big US cities like Boston are so bad, they will barely cover basics like the lighting and other arena costs. Tour managers are begging local radio stations to do giveaways.'

The poor sales come despite the draw of high-profile support act Cee Lo Green.

Riri announced on her Twitter page that she will be announcing a second support act on Friday. 

She suffered similar problems last year when she was forced to cancel dates in Phoenix, Dallas, Atlanta, Denver and Indianapolis on her 'Last Girl On Earth' tour.

No such problems for the singer in the UK though.

Tickets are selling by the bucketload for her forthcoming tour in October, which takes in nine dates at London's O2 Arena.