Britney Spears to hold mystery press conference Thursday

Britney Spears will hold a press conference on Thursday, but even her closest aides have no idea what she's going to announce.

The superstar has invited selected media representatives, journalists and record industry executives to the Los Angeles Convention Center.

The 24-year-old has not revealed what the subject matter of the press conference will be, but it is widely anticipated she will officially announce her second pregnancy with husband Kevin Federline.

Sony executive Karen Phillips says, "Britney hasn't held a press conference in so long that we know it's something big -- pregnancy, a split, we're not sure."

Spears and Federline wed in September 2004 after a whirlwind romance and have an 8-month-old son, Sean Preston, together.

The couple have been plagued by persistent rumors of relationship problems and have not been seen together in the past few weeks.

Jive Records and Spears' management team are reportedly planning to release her fifth album in November, and a world tour is tentatively scheduled for 2007.

Spears was also due to perform at numerous award shows this year, but has since cancelled the commitments without explanation.

sfgate