A federal judge in South Carolina has ordered the release of Jose Padilla, the so-called "dirty bomber," within 45 days if he is not charged with a crime or held as a material witness.

The February 28 order by U.S. District Judge Judge Henry F. Floyd represents the latest challenge to the President's asserted authority to hold U.S. citizens in detention as enemy combatants.

Judge Floyd ruled that Congress had not authorized military detention of a U.S. citizen seized in the country, and that the President cannot constitutionally order such a detention without authorization from Congress.

The government is expected to ask for the release order to be stayed while it appeals the decision.

Padilla's case was among a group of legal challenges to the U.S. Supreme Court relating to certain terrorist detentions.  He has been held without charge as an enemy combatant since his arrest in May 2002.  His case came before the Supreme Court in June 2004, but was dismissed because it was filed in the wrong lower court.