Jack Teixeira, an employee of the US Air Force National Guard, was to make an initial appearance in a Massachusetts federal court, a district court official told AFP.

His dramatic arrest was broadcast live on US TV networks Thursday following a week-long investigation into one of the most damaging leaks of classified information since the 2013 dump of National Security Agency documents by Edward Snowden.

US Attorney General Merrick Garland told reporters Thursday that Teixeira had been arrested "in connection with an investigation into alleged unauthorized removal, retention and transmission of classified national defense information."

News footage of the operation in the southern Massachusetts town of North Dighton 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.

Police in the small town in the northeastern state sought to reassure the community about the heavy law enforcement presence, saying in a statement that there was "no threat to public safety."

The US National Guard Bureau said Teixeira had enlisted 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.

US Defense Secretary Lloyd Austin issued a statement praising the Justice Department and FBI "for their swift arrest in connection with this investigation."

Austin added that he was 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."

Teixeira's arrest came a day after The Washington Post reported that hundreds of pages of documents had been posted on the social media platform Discord by a man who worked on a US military base.

- Top secret material -

According to The New York Times, a "trail of digital evidence" pointed to Teixeira as the leader of the private group on Discord, called Thug Shaker Central, where the documents surfaced.

The embarrassing security breach has revealed US unease over the viability of a coming counteroffensive by Kyiv's forces against Russian troops as well as concerns about Ukrainian air defenses, and pointed to US spying on allies including Israel and South Korea.

President Joe Biden addressed the leak earlier on Thursday during his visit to Ireland, saying he was "concerned".

US media reported that the Biden administration is seeking to beef up its monitoring of social media sites and chat rooms after intelligence agencies failed to spot the leaked documents online for weeks.

The Pentagon has also "begun to limit who across the government receives its highly classified daily intelligence briefs," CNN reported on Thursday.

The alleged leaker reportedly went by the nickname "OG" and regularly posted documents in the chat group in question for months.

The group of around 24 people, including some from Russia and Ukraine, bonded over their "mutual love of guns, military gear and God," and formed an "invitation-only clubhouse in 2020 on Discord," reported the Post -- which like the New York Times cited unidentified members of Thug Shaker Central.

OG told the group members that he spent "some of his day inside a secure facility that prohibited cellphones and other electronic devices," the Post report said.

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, the newspaper reported.

OG had a "dark view of the government," and "spoke of the United States, and particularly law enforcement and the intelligence community, as a sinister force that sought to suppress its citizens and keep them in the dark," the Post said, citing one of the group's members.

A Discord spokesperson told AFP that user safety is a priority, and that content violating its policies can result in people being banned, servers being shut down, and police alerted.

"In regards to the apparent breach of classified material, we are cooperating with law enforcement," the spokesperson said.

"As this remains an active investigation, we cannot provide further comment at this time."

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