Jack Teixeira, 22, orchestrated the most damaging leak of classified information in a decade while serving as an IT specialist with the Massachusetts Air National Guard.

He posted highly sensitive documents on the social media platform Discord, from which they spread across the internet.

"I wanted to say that I'm sorry for all of the harm that I've brought and that I've caused, and that I don't think I can really sum up how contrite I am," Teixeira told the court ahead of sentencing, The Boston Globe reported.

Teixeira, whose family members were in court for the sentencing, was arrested in April 2023 and pleaded guilty in March this year to six federal counts of willful retention and transmission of national defense information.

The United States Attorney for the District of Massachusetts Joshua Levy told a media briefing Tuesday that the platform used by Teixeira reached 150 million people worldwide.

"Jack Teixeira made the deliberate choice day after day, week after week for over a year to share the nation's secrets that were entrusted to him," he said, confirming the sentence of 15 years imprisonment.

Teixeira, who was also ordered to spend three years on supervised release following his prison term and to have no contact with foreign agents, was detained in a dramatic arrest broadcast live on TV networks.

Because he was on active duty at the time of the offenses, he was subject to both federal law and the Uniform Code of Military Justice and consequently he will now face a military trial.

The documents leaked by Teixeira pointed to US concern over Ukraine's military capacity against invading Russian forces, and also showed Washington had apparently spied on allies Israel and South Korea, among other sensitive details.

- 'Exceptionally grave damage' -

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

"By posting intelligence products on the social media platform Discord to feed his own ego and impress his anonymous friends, Teixeira caused exceptionally grave damage to the national security of the United States," prosecutors wrote in a memo ahead of sentencing.

Teixeira's defense team had sought the minimum sentence possible in the case, arguing that the disgraced airman had not sought to harm his country, and also pointing to his autism diagnosis and ADHD condition.

"Jack is still essentially a child -- at the very least, a 'youthful offender' -- who has his whole life in front of him," his defense attorneys argued.

It was the biggest such breach since the 2013 dump of National Security Agency documents by Edward Snowden, and raised serious 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 held a top-secret security clearance since 2021.

Teixeira wrote on social media in November 2022 that he wanted to "kill a ton of people" because it would be "culling the weak minded," the prosecution wrote in a court document.

Ahead of his arrest, prosecutors say Teixeira sought to conceal his crimes by destroying and disposing of his devices and deleting online accounts he had used.