A Libyan militia leader pleaded not guilty to a terrorism charge relating to the attack on the US diplomatic compound in Benghazi that killed four Americans.
Ahmed Abu Khatallah arrived at the US District Court in Washington and was charged with providing material support to terrorism at a hearing in US District Court.
US Ambassador Christopher Stevens and three other Americans died in the September 11, 2012, Benghazi attack.
Libyan Benghazi attack leader Ahmed Abu Khatallah was brought to federal court in Washington from a Navy warship where he has been held since his June 15 capture, according CNN and The New York Times reported.
Khatallah was taken aboard the USS New York, an amphibious transport ship, after his seizure by US special operations forces in a raid on the outskirts of Benghazi. He is expected to be prosecuted in the US criminal justice system.
US Ambassador Christopher Stevens and three other Americans died in the Sept. 11, 2012, Benghazi attack. Khatallah is charged with killing a person on U.S. property, a firearms violation and providing material support to terrorism.
The US attorney's office in Washington has said that the Libyan militia leader suspected in the 2012 attack on the American diplomatic mission in Benghazi that killed four Americans is in federal custody.
A spokesman said: "Ahmed Abu Khatallah is in law enforcement custody," but would not say where he was being held. US officials said Khattallah was expected to arrive in America over the weekend.
The US did not inform the Libyan government about the arrest of the suspected ringleader of the 2012 on an American diplomatic compound, according to a Libyan minister.
The US Ambassador to the United Nations, Samantha Power, notified the UN Security Council of the capture on Sunday of Ahmed Abu Khatallah by US special forces.
She said an investigation had not only implicated him in the 2012 raid but also planned "further armed attacks" against US personnel.
US officials have told the UN Security Council that a suspected ringleader of the deadly 2012 attack on its diplomatic compound in Benghazi had been planning to target more Americans.
In a letter obtained by reporters, the US Ambassador to the United Nations, Samantha Power, notified the council of the capture on Sunday of Ahmed Abu Khatallah by US special forces in Libya.
It came after an investigation identified him as a key figure in the 2012 attack that killed four Americans.
"The investigation also determined that he continued to plan further armed attacks against U.S. persons," Power wrote in the letter,
"The measures we have taken to capture Abu Khatallah in Libya were therefore necessary to prevent such armed attacks, and were taken in accordance with the United States' inherent right of self-defense," she wrote.
The capture of Ahmed Abu Khatallah may be seen as a victory for President Obama, who has been accused by Republicans of playing down the role of al-Qaeda in the 2012 attacks for political reasons and being slow to deliver on promises of justice.
Republicans also said then-Secretary of State Hillary Clinton had failed to take steps to ensure the safety of American diplomatic personnel, an issue that is still resonating as Clinton considers running for US president in 2016.
Clinton defended the decision to put diplomats in dangerous situations on Tuesday but noted that incomplete information increased the risk in Benghazi in 2012.
"We send Americans into perilous dangerous places all the time, and I believe that's the right decision," Mrs Clinton told CNN."We have to do it prudently, of course, but we need to be where things are happening that can affect us."
US officials said America had captured a suspected ringleader of the 2012 attack on the US diplomatic compound in Benghazi, Libya, that killed four Americans including the US ambassador and ignited a political firestorm in Washington.
"Since the deadly attacks on our facilities in Benghazi, I have made it a priority to find and bring to justice those responsible for the deaths of four brave Americans," he said in a statement.
President Barack Obama said in a statement he had authorised the operation in Libya on Sunday, in which US special operations forces captured Ahmed Abu Khatallah.
He later told an audience in Pittsburgh that Khatallah was being transported to the United States.
The United States has captured one of the suspected ringleaders of the 2012 attack in Benghazi, Libya, that killed four Americans including the US ambassador, the Pentagon said.
The suspect was captured on Sunday and is now in US custody outside of Libya, Pentagon spokesman Rear Admiral John Kirby said in a statement.
Officials told The Washington Post Ahmed Abu Khattala was captured by American troops and is "en route" to the US. No American soldiers were injured in the operation, the newspaper claimed.
The diplomatic compound in Benghazi was attacked in 2012 and left US Ambassador to Libya J. Christopher Stevens dead.
The death toll from clashes in the eastern Libyan city of Benghazi has risen to 43 with more than 100 people wounded, a Health Ministry official said today.
Fighting broke out on Friday between irregular military forces and Islamist militants. The situation was quiet on Saturday, residents said.
A security guard and at least five children were injured when a bomb toppled a garden wall outside the Egyptian consulate in Benghazi today, witnesses said.
The guard required hospital treatment, while the children were cut by flying glass, they said.
A building opposite the consulate and a number of vehicles were also damaged in the explosion.