Jack Teixeira, a 22-year-old Massachusetts Air National Guard IT specialist, pleaded guilty in March to sharing the top secret information online, alleged to be the most damaging leak of US classified documents in a decade.

Under the terms of his guilty plea, Teixeira faces some 17 years in prison in return for Department of Justice prosecutors dropping more serious espionage charges that could have resulted in a life sentence.

However, the Air Force announced this month that it would seek to prosecute him in a military tribunal for alleged misconduct related to his duties as a service member.

An initial hearing was held Tuesday at Hanscom Air Force Base, in Massachusetts, an Air Force spokesman confirmed to AFP, without giving any further details.

Teixeira was detained in April 2023 in a dramatic arrest broadcast live on TV networks.

He was accused of posting the documents -- some dated as recently as March 2023 -- to a private chat group on the social media platform Discord.

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

The documents, which soon spread across the internet, pointed to US concern over Ukraine's military capacity against invading Russian forces.

They also showed that Washington had apparently spied on allies Israel and South Korea, among other embarrassing details.

It was the biggest such breach since the 2013 dump of National Security Agency documents by Edward Snowden, and raised tough questions about access by Teixeira and other junior staffers to high-level secrets.

Teixeira was an airman first class -- the third-lowest rank for enlisted US Air Force personnel -- and had possessed a top secret security clearance since 2021.