The arrest, which was not announced at the time, was outlined in an internal bulletin prepared by the Department of Homeland Security and the FBI. It was first disclosed by ABC News.

The report comes a week before Pope Francis’ first trip to the United States where elaborate security measures are being taken for the pontiff’s visits to Washington, New York and Philadelphia.

The law enforcement officials, who are not authorized to discuss the matter publicly, said the boy’s alleged activities in part involved the distribution of information on explosives through social media.

But the activities, the officials said, appeared to represent more of an aspiration to such a plot than a fully formed and imminent threat.

The teenager was not identified, yet the arrest highlights a mounting concern for young people in the United States, who are being exposed to ISIL’s aggressive social media recruiting efforts.