James Bradley, 20, of New York and Arwa Muthana, 29, from Alabama were stopped on Wednesday as they stepped onto the gangplank of a cargo ship in Newark, New Jersey.
The Justice Department said that Bradley had expressed violent extremist views since at least 2019, and in contacts with an undercover law enforcement agency last year repeatedly said he believed in the Islamic State group.
He also told the undercover agent he was willing to carry out an attack against a US target, including possibly the US Military Academy at West Point.
Bradley had already drawn the FBI's attention after a friend of his was arrested in 2019 planning to travel to Afghanistan to join the Taliban, according to a court filing.
Since then, Bradley "has continued to express his desire to carry out violence in support of radical Islamic ideology, directed his support and allegiance to ISIS, and attempted to travel overseas to join and fight for ISIS," the FBI said, using an acronym for the Islamic State group.
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Bradley also shared Islamic State propaganda with the undercover agent, and they discussed his various options for joining extremist groups or launching an attack in the United States.
Ultimately Bradley decided to head to Yemen to link up with the Islamic State with Muthana, a woman he married in January 2021.
"If I don’t find them I just keep going to Somalia," he told the agent, referring to the East African country where the violent, Al-Qaeda-linked Al Shabaab Islamic extremist group menaces the government.
The case demonstrated that jihadist groups still exert a pull on some people in the United States, even after the Islamic State was defeated by US and allied troops in its home base in Iraq and Syria.
"The threat of terrorism at home and abroad remains," said Assistant Attorney General John Demers.
The department "is committed to holding accountable those who would provide material support to foreign terrorist organizations," he said in a statement.
Both Bradley and Muthana face up to 20 years in prison on the charge of conspiring to provide material support to a foreign terrorist organisation.
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