US President Joe Biden has voiced 'concern' over a leak of US documents that the Pentagon has called a risk to national security
US President Joe Biden has voiced 'concern' over a leak of US documents that the Pentagon has called a risk to national security AFP

US President Joe Biden voiced concern Thursday over the leak of a cache of classified military documents, as details emerged of a military base employee who may have first posted the papers online.

The leaks, which the Pentagon have called a serious risk to national security, have revealed US unease over the viability of a coming Ukrainian counteroffensive against Russian forces, and suggested it spied on allies Israel and South Korea.

Images of the documents have circulated on social media platforms for weeks and sparked an uproar since being published by news outlets in recent days.

Two members of a group on the online social platform Discord told The Washington Post that hundreds of pages of material had been posted there by a man who told them he worked on a US military base and brought the documents home with him.

The man, who went by the nickname "OG", regularly posted documents on the group for months, the group members told the newspaper, speaking on condition of anonymity.

Some information in the documents was so sensitive it was marked "NOFORN", meaning it was not to be shared with foreign nationals, The Post reported.

The group of around 24, including people 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," the newspaper reported.

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

He also told them that he "toiled for hours writing up the classified documents to share with his companions in the Discord server," the paper reported.

Later, he began taking photos of the documents and shared those with the group.

"When rendering hundreds of classified files by hand proved too tiresome, he began posting hundreds of photos of documents themselves," The Post reported.

OG had told the other members of the group not to share the documents, and that he had not intended to be a whistleblower, The Post reported, citing one of the friends.

The Post said OG had "a dark view of the government."

"(A group member) said he 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. He ranted about 'government overreach.'"

Dozens of photographs of documents have been found on Twitter, Telegram, Discord and other sites in recent days, though some may have circulated online for weeks, if not months, before they began to receive media attention.

The breach has sparked a criminal investigation by the US justice department and Biden, on a visit to Ireland, said he was concerned about the leak.

"I'm concerned that it happened. But there's nothing contemporaneous that I'm aware of that's of great consequence," Biden said.

"There's a full-blown investigation going on, as you know, with the intelligence community and the Justice Department, and they're getting close."

White House spokeswoman Karine Jean-Pierre said the national security implications are being reviewed.

She said the administration urged social media companies to "avoid facilitating" the distribution of such material.

"We do believe that social media companies have a responsibility to their users and to the country to manage the private sector infrastructure that they create and now operate," she told reporters traveling with Biden.

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," a Discord spokesperson said.

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