The Libyan militant accused of masterminding the deadly Benghazi attacks that have become a flashpoint in U.S. politics appeared briefly for the first time in an American courtroom, pleading not guilty Saturday to a terrorism-related charge nearly two weeks after he was captured by special forces.

In a 10-minute hearing held amid tight security, Ahmed Abu Khattala spoke just two words, both in Arabic. He replied “yes” when asked to swear to tell the truth and “no” when asked if he was having trouble understanding the proceeding.

Abu Khattala became the most recent foreign terror suspect to be prosecuted in American courts, a forum the Obama administration contends is fairer and more efficient than the military tribunal process used at Guantanamo Bay, Cuba. The case was being tried in Washington despite concerns from Republicans in Congress who say he should not be entitled to the protections of the U.S. legal system.

A grand jury indictment handed up under seal Thursday and made public Saturday said Abu Khattala participated in a conspiracy to provide material support and resources to terrorists in the attacks of Sept. 11, 2012, that killed U.S. Ambassador Chris Stevens and three other Americans.

That crime is punishable by up to life in prison. The government said it soon would file more charges against Abu Khattala.

Current and former senior U.S. law enforcement officials briefed on the investigation of Abu Khattala said the next phase of the case — proving the charges against him in federal court — would be particularly challenging because the attacks occurred in a country that is not friendly to the United States.

FBI investigators were not able to visit the crime scenes in Benghazi to collect evidence until several weeks after the attacks because of concerns about security there. The case also relies on testimony from Libyan witnesses who will most likely have to be flown to the United States to testify and who may not hold up well to being cross-examined.

Yet law enforcement officials expressed confidence in the work.

“We have plenty of evidence to convict this guy,” one senior official said.

The violence in Libya on the 11th anniversary of the Sept. 11, 2001, attacks became a political controversy at home.

Republicans accused the White House, as the 2012 presidential election neared, of intentionally misleading the public about what prompted the attacks. The White House said Republicans were politicizing a national tragedy.

U.S. special forces captured Abu Khattala in Libya two weeks ago, marking the first breakthrough in the investigation.

Officials had been questioning Abu Khattala aboard a Navy ship that transported him to the United States. He was flown early Saturday by military helicopter from a Navy ship to a National Park Service landing pad in the city’s Anacostia neighborhood, according to a U.S. official who spoke on condition of anonymity.

A U.S. official said Abu Khattala had been advised of his Miranda rights at some point during his trip and continued talking after that.

A criminal complaint filed last year and unsealed after Abu Khattala’s capture charged him with terror-related crimes, including killing a person during an attack on a federal facility.

Abu Khattala was a prominent figure in Benghazi’s circles of extremists. He was popular among young radicals and lived openly in the eastern Libyan city, spotted at cafes and other public places, even after the Obama administration publicly named him as a suspect.

He is accused of being a member of the Ansar al-Shariah group, the powerful Islamic militia that the U.S. believes was behind the attack.

He acknowledged in January that he was present during the storming of the U.S. mission in Benghazi. But he denied involvement in the attack, saying he was trying to organize a rescue of trapped people.