A Palestinian-born professor will remain jailed without bond until his trial on charges that he led a terrorist organization's U.S. operations and helped its members enter the country, a federal judge ruled today.

Former University of South Florida computer engineering professor Sami al-Arian and co-defendant Sameeh Hammoudeh must remain jailed because each poses a danger and a flight risk, U.S. Magistrate Judge Mark A. Pizzo ruled.

"These two, based on the government's strong presentation, repeatedly assisted, promoted, or managed the [Palestinian Islamic Jihad], an organization which indiscriminately murders to achieve its goals," Pizzo wrote. Pizzo granted bond to two other co-defendants, setting Ghassan Zayed Ballut's at $620,000 and Hatim Naji Fariz's at $1.1 million.

The defendants and four co-conspirators living abroad were indicted on Feb. 20 on racketeering, conspiracy and other charges.

Prosecutors say al-Arian ran the Palestinian Islamic Jihad's U.S. operations and that the other three worked for him. The government says the group is responsible for 100 murders in Israel and its territories.

Al-Arian has said that he has never advocated violence.

Pizzo wrote that the defendants all "publicly preach and practice" nonviolent ideals, and that al-Arian's civic record "is particularly outstanding." But he added that those public actions were at odds with intercepted conversations involving al-Arian and Hammoudeh that promoted violence.

A not-guilty plea was entered on al-Arian's behalf last week. Ballut, Hammoudeh and Fariz have pleaded not guilty.