A judge on Thursday ordered Britney Spears to pay an extra $350 000 in lawyer fees, in her costly legal battle with ex-husband Kevin Federline for custody of their two children.

Judge Reva Goetz' decision comes one month after another judge, Scott Gordon, ordered Spears' conservatorship run by her father to pay $375 000 to Federline's lawyers.

The custody battle, Spears' lawyer told Gordon at the time, has already cost the singer about a million dollars.

Spears shot to superstardom in late 1998 with her smash-hit debut album 'Baby One More Time', which she followed with another chart-topping success the following year, 'Oops! ... I Did It Again'.

But her career has been locked in a downward spiral since her split from Federline in 2006, and their divorce in 2007.

Federline last year was granted temporary custody of their children, two-year-old Sean Preston and Jayden James, aged one.

After Spears was admitted to psychiatric care earlier this year, her father took control of her financial and business affairs at least until 31 July.

AFP