An 18-year-old Minnesotan who is accused of conspiracy to provide material support to the Islamic State group was arrested on Tuesday following an FBI investigation. His friend, a Minnesotan two years his senior, is charged with actually providing that support. He is believed to have joined a terrorist organization in Syria.

"As charged, these two young men conspired to join ISIL and travel from Minnesota to the Middle East to engage in a campaign of terror in support of a violent ideology," said U.S. Attorney Andrew Luger in a statement, referring to the Islamic State group by another name.

Abdi Nur, 20, and Abdullah Yusuf, 18, are Somali Americans who planned to join the extremists' fight in Syria via Turkey, according to the criminal complaint. Yusuf was stopped when he attempted to fly from the Minneapolis-St. Paul airport to Turkey in late May. Nur successfully got on an Istanbul-bound flight the next day, and did not return as scheduled two weeks later.

Including Nur and Yusuf, the United States has charged more than 15 people with "offenses related to the foreign fighter threat in Syria," Assistant Attorney General John Carlin said in a statement. The two Minnesotans aren't the first to be accused of trying to become a part of the Islamic State group. Last month, a man from North Carolina pleaded guilty to attempting to join the group through Lebanon.

Yusuf is expected to appear in court Tuesday afternoon.

In the months before Nur departed for the Middle East, he became "much more religious" and started talking about jihad, the complaint alleges. Before he left, he was in contact with an individual who is believed to be fighting in Syria, the FBI said.

After his departure, Nur used Facebook to communicate with someone in the United States, according to the complaint, sending messages that said he had gone "to the brothers," and that "we will see each other in the afterlife inshallah."

Luger said that dozens of young Somali Minnesotans have aided terrorist organizations since they first began recruiting in the area in 2007. "Unfortunately, Yusuf and Nur were not the first—and may not be the last—to conspire in support of ISIS," Luger said in the statement. "As we work with our many partners to improve the lives of Somali Minnesotans, we will continue to investigate and prosecute aggressively criminals who provide support for terror."