The teen, whose name was not disclosed, was taken into custody last week, the officials said.

Prosecutors are seeking to charge him as an adult but currently have charged him as a juvenile, one of the law enforcement officials said.

The case remains under seal. It was first reported by The Washington Post on Wednesday.

The Post, citing officials and neighbors, reported that investigators spent more than a month watching the teen and his home before he was arrested.

The teen, who lives in a Virginia suburb of Washington, is accused of helping a slightly older adult travel to Syria. The adult is believed to have joined ISIS there, a separate law enforcement official said.

The teen is also accused of distributing ISIS messages to a network of contacts, one of the officials said.

Former boss: He didn't seem radical

The teen is an "intelligent kid," a man who hired him to write for a digital currency news website said Wednesday evening. Dustin O'Bryant, the editor of the website Coin Brief from Alabama, said: "He did not come across as radical in any way."

The teen wrote freelance articles for the website for seven months last year. He was told not to bring religion into his writing, O'Bryant said, adding he had noticed the young man had written online posts about his faith. The teen complied, he said.

The website editor said he was "extremely, extremely surprised" to learn of the arrest from reporters calling him. He hadn't spoken to the teen since February, when the young man said he was dealing with personal matters but wanted to start writing for the website again at some point this year.

Give me two weeks to three months, the boy told him.

O'Bryant said he is shocked by the charge.

"I hope there's some sort of misunderstanding here, and that he didn't know what he was doing," he said.

He added that he didn't realize the teen was in high school because he had college courses on his resume.

U.S. stops some from going to join ISIS

More than 20,000 foreigners have gone to fight for ISIS, the radical Islamist group that controls portions of Iraq and Syria, experts have told Congress.

National Intelligence Director James Clapper said 180 Americans have tried to go to fight in Syria. It's unclear how many of those were attempting to join ISIS. It was also unknown if the man the teen allegedly helped is a U.S. citizen.

Others have been prevented from going there or providing support.

Also Wednesday, a 21-year-old California man arrested last summer was indicted, changed with attempting to support terror and other counts. Adam Dandach, of Orange, California, was accused by the FBI in the indictment of attempting to provide himself and material support to work under the direction and control of ISIS. He will be arraigned March 16.

In February, three men from New York -- Abdurasul Juraboev, 24; Akhror Saidakhmetov, 19; and Abror Habibov, 30 -- were arrested and charged with conspiring to provide material support and resources to a foreign terrorist organization. An unsealed criminal complaint accused one of the men of discussing a potential attempt to assassinate President Barack Obama. One had discussed hijacking a flight and handing it over to ISIS, the complaint said.

Four women from Colorado have been accused of attempting to join ISIS. Three Denver teenagers, who investigators say were recruited via social media, were stopped in Germany in October and sent back to the United States. After being arrested in spring 2014, Shannon Maureen Conley was one of the first Americans sentenced for conspiracy to support ISIS.

Two men who have appeared in horrific ISIS propaganda videos could be from the United States or Canada, according to analysts. The individuals, both of whom are shown wearing masks covering everything but their eyes, spoke in what sounded like North American accents. One was in a video entitled "Flames of War," which shows the execution of a handful of men. The other militant is the speaker in ISIS' first propaganda video out of Libya, which ends with the graphic beheading of more than a dozen Egyptian Christians.