North Dighton, Massachusetts - The Federal Bureau of Investigation (FBI) has arrested a suspect in the investigation into the publication of explosive US intelligence information on the internet.

The man, who has since been identified as Jack Teixeira, was taken into custody in connection with the "alleged unauthorized removal, retention, and transmission of classified national defense information," US Attorney General Merrick Garland said in Washington on Thursday.

The arrested man is "an employee of the United States Air Force National Guard." He was taken into custody "without incident," Garland said. "This investigation is ongoing."

Teixeira was arrested on Thursday afternoon in North Dighton, Massachusetts. He was taken into custody one week after the first news reports of the security breach emerged.

CNN showed video footage of the arrest, with the police taking away a young man wearing a T-shirt and shorts.

US media had previously circulated the first details about the suspected mole. The man is said to have led a chat group on Discord, a platform popular with video gamers.

He had initially shared the documents with the group as transcripts and later uploaded photos of printed documents there. According to US media, he is 21 years old, but Garland did not give his age.

For weeks, secret documents from US agencies – allegedly from the CIA and the Pentagon – have been circulating on the internet about the Russian war in Ukraine, including information about arms deliveries and assessments of the war.

There were also details on alleged US spying operations against partners, but it is unclear what is authentic and what might have been edited.

The leak has embarrassed the US government as it prompts questions about how reliable the United States is, how well it protects its own secrets and those of its partners, and how loyal it is to its allies.

US Secretary of Defense Lloyd Austin said he only found out about the data leak around the time of the initial news reports, even though the material had been floating around the web for weeks.

Pentagon spokesperson Patrick Ryder called the leaks "a deliberate criminal act." Violations of the US Espionage Act can be punished with 10 years in prison.

The Washington Post reported that about two dozen young people with a penchant for weapons and military equipment had come together in the suspect's Discord chat group, which was formed in 2020.

In the chat, Teixeira was said to have gone by the moniker "OG" and was described as a charismatic gun fanatic with dark views of the US government, along with intelligence and law enforcement agencies.

"OG" told his group that he had obtained the documents at a military base where he worked. He said he spent parts of the day in a secure facility where mobiles and other electronic devices that could be used to take photos or videos were banned. At first, he copied the documents and then transcribed them for the chat.

Members of the chat told the Washington Post that when copying proved too tedious, he began posting pictures of the printed documents, which then circulated in other groups and other websites.