The 21-year-old Massachusetts Air National Guard IT specialist was arrested in April for allegedly orchestrating the most damaging leak of US classified documents in a decade.

He is facing six counts of retaining and transmitting national defense information. They each carry sentences of up to 10 years in prison.

Teixeira appeared before Magistrate Judge David Hennessy in Worcester, Massachusetts, on Wednesday and entered a plea of not guilty to each of the charges, according to court documents.

His lawyer asked that Teixeira be released pending trial but the judge denied the request.

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.

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 and showed Washington had apparently spied on allies Israel and South Korea, among other sensitive 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, a junior staffer, 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.

Last month a judge ordered that Teixeira remain in jail pending trial after prosecutors argued he posed an ongoing risk to American national security.

Prosecutors said that Teixeira might still have access to classified documents and that "hostile" nations could aid his escape if he was released from prison.

They also cited his history of making "violent" statements.

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

Prosecutors also said the airman sought advice from another user about what type of rifle would be easy to operate from the back of an SUV, and that he searched mass shootings online.

Teixeira was detained on April 13 in a dramatic arrest broadcast live on TV networks.