A young gamer who led an online chat group has been arrested over an embarrassing leak of top secret documents described as one of the worst intelligence breaches in the US.

The FBI arrested Jack Teixeira, a 25-year-old national guardsman, at home in Massachusetts on Thursday (local time), according to media reports.

Dozens of sensitive US government documents, encompassing Ukraine’s air defences to Israel’s Mossad spy agency, had been leaked onto online chat forum Discord in recent weeks.

It was considered the worst breach since 700,000 documents, videos and diplomatic cables were loaded onto the WikiLeaks website in 2013.

Teixeira’s identity was first revealed in the New York Times. He was named as a member of the Massachusetts Air National Guard.

Teixeira led the online gaming group Thug Shaker Central where about 20 to 30 people shared their love of guns, racist memes and video games, the New York Times said.

It was not immediately clear if Teixeira had a lawyer who could speak on his behalf.

But the NYT said that a man who had been standing outside the Teixeira home said “he needs to get an attorney if things are flowing the way they are going right now. The Feds will be around soon, I’m sure”.

The National Guard did not confirm his identity but said in a statement that “we are aware of the investigation into the alleged role a Massachusetts Air National Guardsman may have played in the recent leak of highly-classified documents”.

The US Department of Justice opened a formal criminal probe last week after the matter was referred by the Pentagon, which is assessing the damage done by the release of classified US information.

The FBI did not immediately respond to a request for comment.

US President Joe Biden earlier on Thursday said investigators were closing in on the source of the leak.

His administration has scrambled for days to contain the fallout from the leaked information, which has publicised potential vulnerabilities in Ukraine’s air defence capabilities and exposed private assessments by allies on an array of intelligence matters.