(CNN) -- U.S. authorities arrested an American man returning from overseas who they say is a sympathizer of the terrorist group ISIS.
Donald Ray Morgan was arrested on August 2 on arrival at New York's John F. Kennedy International Airport from Frankfurt, Germany, according to federal court documents.
A federal grand jury in North Carolina charged him with illegal weapons possession, and prosecutors say he was involved in weapons trafficking in violation of his probation for a previous felony conviction, the court documents show.
The court documents make no mention of the ISIS connection, but U.S. officials say that part of what drew their attention is Morgan's online activities, making Twitter postings in support of the terrorist group.
Morgan is not thought to be involved in any active plots inside the U.S. or elsewhere and instead may be more of an "aspirational" supporter of ISIS.
Still, with the rise of ISIS, and more than 100 Americans believed to have traveled to Syria to fight in the ongoing civil war, the FBI is on alert for returning Americans who may be associated with groups fighting there.
The New York Daily News reported Sunday night that at his first appearance in court on August 4, prosecutors opposed bail, citing fears that he was possibly involved with ISIS, which is fighting to establish an Islamic extremist state in parts of Syria and Iraq. The group calls itself the Islamic State but formerly was known as the Islamic State in Iraq and Syria.
The Daily News report cited officials alleging that Morgan used the moniker Abu Omar al Amreeki to publish tweets in support of ISIS while he spent time in Lebanon. The newspaper quoted federal prosecutor Nadia Moore as saying in court: "It's possible that he traffics in guns to people in this organization (ISIS)."
Chief Magistrate Judge Steven Gold denied bond based on the government's argument, saying the tweets had "clearly implied to me that he is trying to go to Syria or Iraq," according to the Daily News.
A public defender assigned to represent Morgan said there was no evidence Morgan tried to support ISIS, the Daily News reported. The public defender didn't immediately respond to a request for comment from CNN late Sunday.
Morgan is being transferred to Greensboro, North Carolina, to face the weapons charge, court documents show.
ISIS recruiting on the rise in Sunni areas of Iraq