Federal authorities have unsealed an indictment charging a Kenyan man with trying to stage a 9/11-style attack on the United States on behalf of the terrorist organization al-Shabab. Cholo Abdi Abdullah, 30, who was arrested in the Philippines in 2019, was transferred to U.S. custody Tuesday on charges he conspired to hijack an aircraft and slam it into a building.

Abdullah pleaded not guilty to the charges, CBS News senior investigative producer Pat Milton reports. He was arraigned via video at the Manhattan federal courthouse and is being held without bail.

Prosecutors said Abdullah got flight training in the Philippines and obtained a pilot’s license in preparation for an attack.

“This case, which involved a plot to use an aircraft to kill innocent victims, reminds us of the deadly threat that radical Islamic terrorists continue to pose to our nation,” Assistant Attorney General for National Security John Demers said in a statement.

Acting Manhattan U.S. Attorney Audrey Strauss called it a “chilling callback to the horrific attacks of September 11, 2001.”

Abdullah, prosecutors said, started planning the attack in 2016 under the direction of an al-Shabab commander who was also involved in planning a deadly attack in 2019 on a hotel in Nairobi, Kenya.

The State Department has designated the Somalia-based militant group al-Shabab, an al-Qaida affiliate, as a foreign terrorist organization.

He also researched potential hijacking methods and how to get a U.S. visa.

The name of an attorney in the U.S. who could speak on Abdullah’s behalf was not immediately available.