A young Mississippi man pleaded guilty Friday to a terrorism-related charge, months after authorities said he and his fiancee thought about using their honeymoon as ruse to go to Syria to join the Islamic State.

Muhammad Dakhlalla, 23, pleaded guilty to providing material support to terrorism and faces up to 20 years in prison, $250,000 fines and lifetime probation. His sentencing date hasn't been set.

His fiancee, Jaelyn Delshaun Young, is accused in new court documents of being the mastermind of the plan to join the Islamic State. Her trial is set for June 6.

Both remain jailed without bail in Oxford.

The couple was arrested Aug. 8 before boarding a flight from Columbus, Mississippi, with tickets for Istanbul. Authorities say they contacted undercover federal agents last year, seeking online help in traveling to Syria. The two, at one point, told federal agents posing online as recruiters for the Islamic State that they planned to disguise their journey to Syria as a honeymoon.

The couple's arrest stunned their families.

Dakhlalla is a 2011 psychology graduate of Mississippi State University who grew up in Starkville, a son of a prominent figure in the college town's Muslim community. He is the youngest of three sons and was preparing to start graduate school at Mississippi State.

Young, a sophomore chemistry major from Vicksburg, was the daughter of a school administrator and a police officer who served in the Navy reserve. She was a former honor student, cheerleader and homecoming maid at Warren Central High School.

Court papers filed with the plea portray Young as the mastermind of the couple's attempt to join the Islamic State, saying she had already expressed an interest in converting to Islam even before she began dating Dakhlalla in late 2014.

The papers confirm that both Young and Dakhlalla left farewell letters "that explained they would never be back, with Young acknowledging her role as the planner of the expedition and that Dakhlalla was going as her companion of his own free will."

The court papers reiterate earlier government claims that Dakhlalla, in online contacts, told an FBI employee that he was good with computers and media and wanted to contribute to the Islamic State's struggle. Court papers say Dakhlalla said online that he wanted to become a fighter and learn "what it really means to have that heart in battle."

The plea agreement drops a related charge against Dakhlalla, cutting the possible length of any imprisonment. However, in the plea agreement signed Wednesday, Dakhlalla and his lawyer acknowledged that the sentencing recommendation would be adjusted upward because terrorism is involved.