Abu Ghaith was a high school teacher and preacher at a mosque in Kuwait, the U.S. Treasury says on its website. "He fought in Afghanistan, accused the U.S. government of killing children in Iraq through U.N. sanctions, and joined Muslim guerillas fighting in Bosnia-Herzegovina in the summer of 1994."

He was later banned from his mosque for using his sermons to attack the government.

Before September 11, 2001, "his mission was to recruit elements for training in bin Laden's camps in Afghanistan."

The U.S. 9/11 Commission said Abu Ghaith "reportedly" supported the idea of a major operation directly against the United States in 2001.

Bin Laden, leader of the terrorist al Qaeda network that staged the 9/11 attacks on the United States, was killed in a U.S. Navy SEAL raid in Pakistan in 2011.

According to the indictment unveiled Thursday, Abu Ghaith was engaged in planning and perpetrating a federal crime of terrorism against the United States and its citizens. He could face a life sentence if convicted.

In May 2001, Abu Ghaith urged individuals at a guest house in Kandahar, Afghanistan, to swear allegiance to bin Laden, according to the charges. A day after 9/11, the alleged spokesman warned the United States and its allies that a "great army is gathering against you" and called on "the nation of Islam" to battle "Jews, the Christians and Americans," the indictment states.

Abu Ghaith later warned "the storms shall not stop, especially, the airplane storms" and warned Muslims and foes of the United States not to board aircraft or live in high-rise buildings, according to the indictment.