The high court agreed to hear an Obama administration appeal seeking to reinstate a 2006 law providing for the continued detention of "sexually dangerous" convicted federal inmates who have served their prison terms.

A U.S. appeals court based in Virginia struck down the law for exceeding the limits of congressional authority and intruding on police powers Constitution reserves for the states, many of which have similar laws.

The law had been challenged by five inmates who had been kept in custody at a federal prison hospital in North Carolina after their sentences ended.

The U.S. Justice Department said a total of 95 inmates have been identified as possible candidates for post-sentence detention under the law.

In 1997, the Supreme Court ruled the states could confine dangerous sex offenders to mental institutions after they serve their sentences.

Many state laws provide for the commitment under civil law of mentally ill sex offenders who pose a risk of committing more crimes involving children if released into the community.

The federal law defined "sexually dangerous" as someone who suffers from a serious mental illness, abnormality or disorder and would have difficulty in refraining from sexually violent conduct or child molestation, if released.