A chatroom on Discord, a popular social media platform, is suspected to be the source of a major leak of classified U.S. documents that has caused a stir in Washington and revealed previously unknown information about intelligence gathering.

Held on the platform, which hosts real-time voice, video and text chats, a discussion originally created to talk about a range of topics turned to the war in Ukraine.

As part of debates about Ukraine, according to one member of the chat, an unidentified poster shared documents that were allegedly classified, first typing them out with the poster's own thoughts, then, as of a few months ago, beginning to post images of papers with folds in them.

The posts appear to have gone unnoticed outside of the chat until a few weeks ago, when they began to circulate more widely on social media and get picked up by major news outlets. The leaks have alarmed U.S. officials and sparked a Justice Department investigation.

The records have provided startling and surprisingly timely details of U.S. and NATO assistance to Ukraine. They also provided clues about efforts to assist Ukraine in its war with Russia, including an anticipated spring offensive.

The scale of the exposure has yet to be determined. Also unclear is whether any government worked to share the documents or manipulate them.

Asked Monday if the U.S. government was effectively waiting for more intelligence documents to show up online, National Security Council spokesman John Kirby replied: "The truth and the honest answer to your question is: We don’t know. And is that a matter of concern to us? You’re darn right it is."

Chris Meagher, top spokesman for the Pentagon, urged caution in "promoting or amplifying any of these documents," adding that "it does appear that slides have been doctored."

But the breach underscores the difficulties the U.S. and other governments face in securing classified information. Congressional reviews and experts have long warned of weaknesses in U.S. counterintelligence, of the challenges of monitoring an estimated 3 million people with security clearances, and of agencies producing and over-classifying so much information that the U.S. cannot reliably control it.

"I think that the intelligence agencies have adjusted and gotten better at preventing all sorts of mass electronic leaks," said Kellen Dwyer, a former Justice Department prosecutor who was part of the team that brought a federal case against WikiLeaks founder Julian Assange. "But clearly, they haven’t gotten good enough."

The Associated Press interviewed a person who said he was a member of the Discord chat group in which documents appeared for several months. The person, who said he was 18 years old, refused to give his name, citing concerns for his personal safety.

The AP could not independently confirm many details shared by the person, and the original chatroom has been deleted.

The AP reviewed images of documents that appeared in recent weeks in the discussion forums. They include a top-secret analysis of deepening intelligence service ties between Russia’s FSB and agencies in the United Arab Emirates (UAE), the oil-rich Persian Gulf nation that hosts a U.S. air base and cooperates on many security matters with Washington.

Citing signals intelligence, the March analysis says officers from the FSB were caught claiming that the UAE had agreed with Russia "to work together against US and UK intelligence agencies."

A spokesman for the Emirati government said the allegations "are categorically false." U.S. officials at several agencies declined to comment on the document.

"Wild card" scenarios

The AP also saw an analysis of what might happen in the Russia-Ukraine war in certain "wild card" scenarios, including if Russian President Vladimir Putin or Ukrainian President Volodymyr Zelenskyy were to die. The analysis is marked secret, a lower level of classification than top-secret.

Were Putin to fire his top military advisers and the war to escalate, the document speculates he might authorize the use of tactical nuclear weapons if "elites question Putin’s decision-making and Russian forces are unable to overcome manning and equipment shortfalls."

The death of Zelenskyy, in a worst-case scenario, might prompt Europe to restrict weapons shipments, the document says. But a "high-profile Ukrainian leader" might also retain domestic and foreign support as well, it says.

The investigative journalism organization Bellingcat, which specializes in digging through social media and open-source records, interviewed the same person and two others in the Discord chatroom, called "Thug Shaker Central."

Bellingcat reported Saturday that documents from Thug Shaker Central appear to have been shared in another chatroom, "WowMao." From WowMao, the documents appear to have spread more widely – and eventually became the subject of a story in The New York Times on Thursday, which first reported that the Pentagon was investigating a breach.

The Discord user who spoke to the AP on condition of anonymity says he was on a call with others – including the person who for months had been posting documents they said were classified – when the Times story broke.

"We all just kind of lost it," the Discord user said. "We couldn’t believe what was happening."

The person said his primary motivation for speaking to the media was to clear the reputation of a third person, who uses the screenname "Lucca." Posts from Lucca featuring many of the documents were widely shared on Twitter and other social media. Those documents were reported on by The New York Times, The Washington Post and other media outlets.

Lucca "is just a kid," said the poster who spoke to the AP. "He was just consistently posting it to mess with people."

The poster declined to identify the person who originally uploaded the documents to Thug Shaker Central or confirm whether that person worked for the U.S. government. He referred to the original uploader with a nickname, "the O.G."

But the poster said the person who first posted the documents did not appear to be driven by ideology or to expose government secrets broadly, but rather to impress people in their group.

Were that person to be arrested, the poster said he had copies of "way past hundreds" of pages of files.

He wanted to protect fellow posters in the now-defunct chat but also believed the documents contained secrets that Americans should know.

"On the off chance that the O.G. gets arrested, I’m leaking them all," the poster said.