NEW YORK (AP) -- A Somali teenager accused of leading a pirate attack on an American cargo ship off the coast of Africa has pleaded not guilty to piracy charges.

A somber-looking Abdiwali Abdiqadir Muse entered the plea during a brief appearance in federal court in Manhattan.

Afterward, his lawyers said Muse has been kept in solitary confinement since being captured -- a predicament they say has left him scared and confused. They continue to deny the U.S. government's claim that their client is 18. His family has said Muse is as young as 15.

Authorities say Muse was the only surviving pirate among a group that attacked the U.S.-flagged Maersk Alabama on April 8.

Muse was indicted earlier this week on 10 counts including piracy and hostage-taking. If convicted of the most serious charge, he faces a mandatory life sentence.

Muse was ordered to return to court on Sept. 17.

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