The arrest comes a week after the leaks first became widely known, setting Washington on edge about the damage they may have caused. The episode embarrassed the U.S. by revealing its spying on allies and purported Ukrainian military vulnerabilities.

The leak of documents, posted largely on social media sites, was believed to be the most serious security breach since more than 700,000 documents, videos and diplomatic cables appeared on the WikiLeaks website in 2010.

Teixeira was an airman 1st class at Otis Air National Guard Base in Massachusetts, according to his service record.

He joined the Air National Guard in 2019 and worked as a "Cyber Transport Systems Journeyman," or an IT specialist.

Attorney General Merrick Garland told reporters Teixeira was wanted "in connection with an investigation into alleged unauthorized removal, retention, and transmission of classified national defense information."

The FBI said its agents had conducted "authorized law enforcement activity at a residence in North Dighton, Massachusetts."

Aerial news video showed Teixeira with his hands laced behind his head, walking backward toward the armored car with one officer watching from the turret.

He was handcuffed and placed in the back of the vehicle. Garland said he was taken into custody "without incident."

The Justice Department did not say what charges Teixeira would face, although they will likely involve criminal charges of willfully retaining and transmitting national defense information.

Brandon Van Grack, a former Justice Department national security prosecutor now with the law firm Morrison Foerster, said the likely charges could carry up to 10 years' imprisonment, even if Teixeira did not intend to cause harm.

"This is someone who is facing on the higher end of exposure for years in prison ... because the leaks were so damaging," Van Grack said.

Defense Secretary Lloyd Austin said in a statement a Pentagon task force had been "working around the clock to assess and mitigate any damage."

Teixeira was expected to appear in court on Friday, a spokesperson for the U.S. Attorney's Office in Boston said.

A police road block on the way to the house where Teixeira was arrested kept neighbors away from their homes.

One was Dick Treacy, who said he saw officers arriving as he left to go shopping in the early afternoon.

"There were about six to eight army guys with rifles walking around," Treacy said. "This is a very quiet area."

Eddy Souza, 22, said he grew up nearby and that he knew Jack Teixeira when both attended Dighton-Rehoboth Regional High School several years ago.

Souza said Teixeira had expressed no extremist sentiments when they were last in touch several years ago.

"He's a good kid, not a troublemaker, just a quiet guy," Souza said. "It sounds like it was a stupid kid's mistake."

Although the leak only garnered widespread attention after an April 6 story in the New York Times, journalists have found evidence that the documents – or at least some of them – had been floating around on social media as far back as March or even January.

Bellingcat, the Washington Post and The New York Times have traced the documents' earliest appearance to a defunct server on the instant messaging site Discord.

In a chat group on the site, Teixeira went by the handle OG and was admired by the group's mostly young members, who shared a love for guns and military gear.

The Justice Department opened a formal criminal probe last week, after a referral from the Defense Department, which called the leak a "deliberate, criminal act."

Reuters has reviewed more than 50 of the documents, labelled "Secret" and "Top Secret" but has not independently verified their authenticity.

The number of documents leaked is likely to be over 100.

A number of countries have questioned the veracity of some of the leaked documents, including Britain, which said there was "a serious level of inaccuracy" in the information.

The leaks revealed information about allies including Israel, South Korea and Turkey.

US officials believe most of the materials are genuine. Some, however, appear to have been altered to show inflated estimates for Ukrainian battlefield casualties in the war with Russia as well as understated numbers for Russian forces.