Britney Spears' estranged husband Kevin Federline is reportedly refusing to sign their divorce papers while the troubled singer continues to party. Spears embarked on several months of hard partying following her November split from the aspiring rapper, during which she was photographed without underwear, hit a photographer's car with an umbrella and shaved her head.

After checking into rehab in February and leaving the following month, Spears has returned to the Hollywood party scene, much to the chagrin
of her family and estranged spouse.

Sources tell entertainment network E! that Federline is refusing to sign the couple's divorce papers because he is concerned about the well-being of their two young sons, Sean Preston, 21 months; and Jayden James, 10 months.

A source says, "It's not about the money. It's about her partying. It's her partying ways that is forcing Kevin to put his foot down."

Although the divorce is yet to be settled, the couple reached a "global divorce settlement on all issues of their marriage" in March. The agreement meant the two boys would spend most of the week with Spears, but the couple would share joint legal and physical custody of the tots.

However, Spears' behavior since coming out of rehab has reportedly concerned Federline so much, he is seeking a revision of the document.

- Britney Spears Gallery

(This news article provided by World Entertainment News Network)