Washington (CNN) -- Ahmed Abu Khatallah, the man the U.S. accuses of being the ringleader in the deadly 2012 attack on the American diplomatic mission in Benghazi, Libya, pleaded not guilty Saturday during a brief appearance in federal court in Washington.
Abu Khatallah, with long graying hair and a beard, spoke quietly in Arabic with a translator as he was charged with one count of providing material support to terrorists. A federal grand jury returned a single-count indictment Thursday in connection with attacks that killed four Americans, including U.S. Ambassador to Libya Chris Stevens.
Standing before U.S. Magistrate Judge John M. Facciola, Abu Khatallah appeared subdued and briefly looked around the nearly full courtroom. Wearing a dark gray hooded track suit and sandals, the defendant addressed the court only once to say his name in a barely audible voice.
Abu Khatallah was appointed a public defender, Michele Peterson, who entered a not guilty plea. He was ordered to remain in custody until hearings set for July 2 and July 8.
"Now that Ahmed Abu Khatallah has arrived in the United States, he will face the full weight of our justice system," U.S. Attorney General Eric Holder said. "We will prove, beyond a reasonable doubt, the defendant's alleged role in the attack that killed four brave Americans in Benghazi."
Abu Khatallah was indicted by a federal grand jury on a charge of "conspiracy to provide material support and resources to terrorists, knowing and intending that these would be used in preparation for and in carrying out a killing in the course of an attack on a federal facility, and the offense resulted in death," according to Holder's statement.
The single count is part of a legal strategy by federal prosecutors, who plan to file additional charges later, according to U.S. officials. The aim is to delay releasing to the public and Abu Khatallah's lawyer the FBI affidavit detailing the evidence the government has against him.
The investigation is ongoing and the Justice Department can bring additional charges, the statement said.
An earlier criminal complaint in July 2013 said the FBI believed it had evidence to charge him with murder and firing a weapon at the scene of the Benghazi attacks. Those additional charges, if formally added, could bring the death penalty.
In his court appearance, Abu Khatallah, a Libyan national who the government said is about 43, requested consular assistance from the Libyan government. U.S. authorities were working with Libyan embassy officials in Washington to provide him the assistance.
He had been interrogated aboard the USS New York after being captured earlier this month. Though he was interrogated both before and after he had been advised of his Miranda rights, he provided information to interrogators after being advised of those rights, a U.S. official told CNN.
On Saturday, he was flown by helicopter from the ship, an amphibious transport dock, to the nation's capital and driven to the federal courthouse.
After the hearing, Abu Khatallah was taken away under armed guard from the federal courthouse in downtown Washington, a few blocks from the U.S. Capitol and near the White House.
He was then moved to the detention center in Alexandria, Virginia, which is across the Potomac River from the capital.
Authorities say Abu Khatallah is among the senior leaders of Ansar al Sharia, whose members were among several militias that participated in the attacks on U.S. government facilities in Benghazi on September 11-12, 2012.
The attacks spawned a political controversy in the United States because some Republican lawmakers claim the Obama administration tried to mislead the public about them and should have done more to prevent them. The GOP critics say they plan to make Benghazi an issue for former Secretary of State Hillary Clinton, under whose watch the attacks occurred, should she decide to run for president.
The criminal investigation led by the FBI has been extraordinarily challenging, authorities say, in part because lack of Libyan government control in the city prevented investigators from visiting the crime scene for weeks.
U.S. officials, however, say they collected surveillance video, phone eavesdropping and witness statements to bring charges against Abu Khatallah and others involved. They are charged in a criminal complaint in federal court in Washington.
Abu Khatallah became the face of the militant attack, and a top target for the U.S., after he cultivated a celebrity profile in the wake of the attacks, meeting with journalists and granting interviews. He denied to CNN's Arwa Damon that he participated in the attacks.
U.S. military commandos captured Abu Khatallah in a nighttime raid June 15-16. U.S. intelligence assets concocted a ruse to lure him to a villa where the Americans surprised him. The commandos, accompanied by several FBI agents, came ashore by boat and quickly took him away. He remained on the USS New York, undergoing questioning by a team from the FBI-led High-Value Detainee Interrogation Group, until he was taken to court on Saturday.
CNN's Ray Sanchez contributed to this report.