Jose Padilla, a U.S. citizen who was held for more than three years as an "enemy combatant," pleaded not guilty Thursday to criminal charges alleging he was part of a secret network that supported Muslim terrorists.

The plea, followed by a judge's refusal to set bail for Padilla, came one week after he was transferred from military to civilian custody. His trial was set for early September.

"Absolutely not guilty," said Michael Caruso, one of Padilla's lawyers. Padilla did not speak during the hearing, other than to confirm the pronunciation of his name (puh-DIL-uh).

In denying bail, U.S. Magistrate Judge Barry Garber sided with prosecutors who said Padilla likely would flee and that the charges — including allegations that he attended an Al Qaeda training camp in Afghanistan — made him dangerous.

"How much more dangerous can someone be than someone who attended a terrorist training camp?" prosecutor Stephanie Pell said.

Padilla, 35, was arrested at Chicago's O'Hare Airport in May 2002 and held at a military brig without criminal charges, initially on suspicion of plotting to detonate a radioactive "dirty bomb" inside the U.S.

His case raised questions about whether U.S. citizens detained on American soil could be held without trial in the name of the war on terrorism.

Before the Supreme Court could decide whether to take up Padilla's case, the government presented the case to a civilian grand jury, which indicted him in November. The charges do not involve the "dirty bomb" allegations or claims that he plotted to blow up U.S. apartment buildings.

Last week, the high court approved Padilla's transfer to civilian custody in Miami, overruling a lower court that suggested the administration changed tactics to avert a Supreme Court ruling. The justices were scheduled to meet Friday to discuss whether to take up the case, according to attorneys on both sides.

Padilla, a former Chicago gang member and Muslim convert, could be sentenced to life in prison if convicted of conspiring to murder U.S. nationals and providing material support to terrorists.

Caruso, Padilla's lawyer, questioned the strength of the government's case. He said there is insufficient proof to the government's claim that Padilla actually filled out an application to attend an Al Qaeda camp.

Padilla, who lived for a time in Broward County in the 1990s, is charged in the Florida case along with four others.