US Air National Guardsman Suspected Of Leaking Intel To Be Arrested Thursday -source

An Air National Guardsman suspected of leaking highly classified U.S. documents that have embarrassed Washington with allies around the world will be arrested on Thursday in Massachusetts, a source familiar with the situation told Reuters.

The source, who spoke on condition of anonymity, did not elaborate. A spokesperson for FBI headquarters did not respond to a Reuters request for comment.

U.S. President Joe Biden earlier on Thursday said investigators were closing in on the source of the leak in what is believed to be the most serious security breach in years.

Separately, the New York Times reported that the leader of an online group where the secret documents were posted is a member of the Massachusetts Air National Guard.

It named him as Jack Teixeira, a National Guardsman who led Thug Shaker Central, an online group where about 20 to 30 people shared their love of guns, racist memes and video games. The Times cited interviews and documents it reviewed. Reuters could not immediately confirm the guardsman's identity.

The U.S. Department of Justice opened a formal criminal probe last week after the matter was referred by the Pentagon, which is assessing the damage.

Some of the most sensitive leaked details are purportedly related to Ukraine's military capabilities and shortcomings, and information about U.S. allies including Israel, South Korea and Turkey.

Reuters has reviewed more than 50 of the documents, labeled "Secret" and "Top Secret" but has not independently verified their authenticity. The number of documents leaked is likely to be over 100.

Biden, on a three-day tour of Ireland, said he was not overly concerned about the leak.

"There's a full-blown investigation going on, as you know, with the intelligence community and the Justice Department, and they're getting close but I don't have an answer," Biden told reporters.

"I'm not concerned about the leak, I'm concerned that it happened but there is nothing contemporaneous that I'm aware of."

The FBI Washington field office is leading the investigation, according to a person familiar with the matter.

A man with the same name as that mentioned by the New York Times, Jack Teixeira, was promoted to Airman 1st Class last July, according to a post on the 102nd Intelligence Wing's official Facebook page. The unit did not immediately return an email seeking comment.

A number of countries have questioned the veracity of some of the leaked documents, including Britain, which said there was "a serious level of inaccuracy" in the information.

The person who leaked the documents is a gun enthusiast in his 20s who worked on a military base, the Washington Post reported on Wednesday, citing members of an online chat group.

SOURCE OF LEAK

The Post based its report, which did not name the person, on interviews with two members of the Discord chat group. Discord said in a statement that it was cooperating with law enforcement.

Reuters was unable to verify details of the report. Its broad outlines - that the documents were first shared on a Discord server for gun and ammo enthusiasts who often swapped offensive jokes - were initially reported by Netherlands-based investigative journalism group Bellingcat last week.

Since the leak first came to light in March, investigators have been pursuing theories ranging from someone simply sharing the documents to show off the work they were doing to a mole inside the U.S. intelligence community or military.

The leaks have drawn responses from foreign partners of the United States.

On Sunday, Israeli Prime Minister Benjamin Netanyahu's office labeled as "mendacious and without any foundation whatsoever" a document asserting that the Mossad intelligence agency encouraged recent protests against him.

A South Korean presidential official said on Sunday the country planned to discuss "issues raised" in the leaked documents with Washington.