But Sheikh, 29, a permanent U.S. resident living in central North Carolina, was adamant, according to a federal affidavit, telling the informant: “I’m serious” and “Akhi Wallahi!” — Arabic for “Brother, I swear to God!”

Now Sheikh is under arrest on allegations of attempting to reach Syria to provide material support to Al Nusra Front, an Al Qaeda-affiliated group in Iraq that the U.S. deems a terrorist organization.

He was detained Nov. 2 as he arrived at the Raleigh-Durham airport carrying a boarding pass and a one-way ticket. He checked his luggage, cleared two security checkpoints and was about to reach the gate when he was arrested.

A federal grand jury indicted him Nov. 4, and the charges were unsealed Tuesday. The resident of Cary, N.C., is the latest in a string of young men living in the U.S. who have been arrested for trying to join terrorist groups in Syria’s civil war.

In August, Gufran Ahmed Kauser Mohammed, a naturalized U.S. citizen, and Mohamed Hussein Said, a Kenyan, were indicted in South Florida on allegations of conspiring to provide money and recruits for Al Nusra. In September, U.S. Army veteran Eric Harroun agreed to a secret plea deal in Virginia after returning from Syria, where he fought alongside Al Qaeda affiliates.

Sheikh’s activities were unusually brazen — or foolish — because he communicated regularly for weeks through Facebook private messages with two FBI undercover operatives. His postings allegedly included links to a YouTube video of Muslims being invited to fight in Syria, and a photo of a woman in a burka aiming a rifle. “British women are joining the jihad in Syria,” the caption read.

According to the indictment, Sheikh planned to fly to Lebanon and wanted assistance from the undercover agents in getting across the border into Syria. He tried to sell his car to raise money, the charges state, and had acquired heavy work boots and a sleeping bag. He was shopping for a backpack.

He allegedly told an informant that he wanted to “help the mujahedin” any way that he could. He faces up to 15 years in prison and a $250,000 fine. The Al Nusra group has claimed responsibility for nearly 600 attacks in Syria, many of which have killed numerous civilians.

Sheikh’s Facebook messages began in April, the affidavit says, and by September he was deeply involved with the two undercover agents. Asked how he wanted to help the terrorist group, Sheikh allegedly responded that he would provide logistics, assist in drawing media attention to the cause and “fight too, God willing.” He allegedly said he would feel like a hypocrite if he did not join a jihad in Syria.

But he also expressed disappointment that he could not borrow funds from a sister, and worried that he would miss his parents.

To prove his resolve, he emailed a photograph of himself to one of the agents. When he did not hear back quickly enough, he complained, prompting the undercover agent to ask whether Sheikh was being overly anxious. “Heck yeah,” Sheikh reportedly responded.

richard.serrano@latimes.com