Thirteen Somalis and a man from Yemen pleaded not guilty to piracy, kidnapping and firearms charges Tuesday in the February hijacking of a yacht that left four Americans dead.

They entered their pleas in federal court in Norfolk, where five other men convicted of piracy in a separate case last year had been sentenced to life in prison a day earlier.

"There's nothing I know about these charges. I do not admit that I was a pirate," Mohamud Salad Ali said through an interpreter Tuesday.

Each of the men requested a jury trial and all were ordered to remain jailed until then by Magistrate Judge Tommy Miller, who said they are a threat to society and a flight risk.

A trial has been set for May 17, although prosecutors want it pushed back because trying such cases is complicated.

Pirates have rarely been charged in the U.S. The case against the five Somalis sentenced Monday for attacking the USS Nicholas was the first to go to trial since the Civil War, when a New York jury deadlocked on charges against 13 Southern privateers.