Kevin Federline is seeking sole custody of his two children because Britney Spears is keeping their location a secret from him, a spokesperson has claimed.

While Federline has been touring North America to promote his debut album since his marriage split was announced, Spears has been spotted spending time in New York City with neither of their children in sight.

"He's on a bus to Baltimore and doesn't know where the kids are," Michael Sands, spokesman for Federline's lawyer Mark Kaplan, told the New York Post.

"Perhaps you understand now why he's asking for full custody."