Jack Teixeira was arrested Thursday following a week-long probe into the leak of documents which unveiled US concern over Ukraine's ability to fend off the Russian invasion, and showed Washington has spied on allies Israel and South Korea.

It is the biggest such breach since the 2013 dump of National Security Agency documents by Edward Snowden and raises tough questions over the access of junior official Teixeira to high-level secrets.

Teixeira, who wore a beige jumpsuit and appeared glum at his first court appearance in Boston, was charged with the "unauthorized retention and transmission of national defense information."

He is also accused of the "unauthorized removal and retention of classified documents or material." The counts carry prison sentences of 10 years and five years respectively.

At one point during the short hearing his father shouted out, "We love you Jack," to which Teixeira responded: "Love you too Dad."

He was not required to enter a plea and was detained pending a detention hearing set for next Wednesday.

US Attorney General Merrick Garland said there were "very serious penalties" associated with the crimes.

"People who sign agreements to be able to receive classified documents acknowledge the importance to the national security of not disclosing those documents, and we intend to send that message how important it is to our national security," he added.

Teixeira is suspected of posting the documents, some dated as recently as early March, to a private chat group on the social media platform Discord.

The New York Times reported that Teixeira was the leader of the group called Thug Shaker Central and reportedly posted the documents under the nickname "OG".

He first wrote down the contents of classified documents to share with the group, but later began taking photos, telling other members not to share them, according to the Washington Post.

Some of the documents later appeared on other sites, including Twitter, 4Chan and Telegram.

- Military family -

Investigators have not yet suggested what Teixeira's motive was.

He enlisted with the US Air Force National Guard in September 2019 and was an IT and communications specialist who reached the rank of airman first class -- the third-lowest for enlisted air force personnel.

Friends of Teixeira described him to the Washington Post as a devout Catholic and libertarian who is interested in guns.

The newspaper reported that he comes from a family with decades of military service. His father spent 34 years in the same military unit as his son while Teixeira's mother worked for non-profit organizations that support veterans.

Teixeira's dramatic arrest at his home in the southern Massachusetts town of North Dighton was broadcast live on US TV networks Thursday.

Helicopter footage of the operation showed the suspect dressed in red shorts and a T-shirt with his hands behind his head, backing slowly toward rifle-armed, camouflage-clad law enforcement personnel who took him into custody.

A court affidavit by an FBI agent released Friday said that Teixeira had possessed top secret security clearance since 2021.

US Defense Secretary Lloyd Austin has said he is ordering a "review of our intelligence access, accountability and control procedures within the (Defense) Department to inform our efforts to prevent this kind of incident from happening again."

str-pmh-wd-pdh/st