A US Army private confessed to sharing secret information with a satanic neo-Nazi group in a plot to attack his own military unit while it was overseas and to cause “the deaths of as many of his fellow service members as possible,” federal prosecutors in Manhattan said Monday.

The private, Ethan Phelan Melzer, was charged in an indictment unsealed this week with collaborating with the Order of the Nine Angles, or O9A, a group that prosecutors described as “an occult-based neo-Nazi and racially motivated violent extremist group.”

“Ethan Melzer, a private in the US Army, was the enemy within,” said Audrey Strauss, the acting US attorney in Manhattan, a job she moved into over the weekend after her predecessor, Geoffrey S. Berman, resigned under pressure from Attorney General William Barr.

Melzer, Strauss added, had tried “to orchestrate a murderous ambush on his own unit by unlawfully revealing its location, strength, and armaments to a neo-Nazi, anarchist, white supremacist group.”

The FBI and the Army foiled the plot in late May before it could be carried out, prosecutors said, and Melzer, 22, of Louisville, Kentucky, was arrested on June 10.

While he was in custody, he declared himself to be “a traitor against the United States” and said his plan to stage an assault against an unidentified military base was “tantamount to treason,” prosecutors said.

Federal prosecutors said that O9A, which, like other extremist groups, often communicates via encrypted apps like Telegram, espoused “a diabolical cocktail of ideologies laced with hate and violence.”

Experts have said the group, which is based in Britain, overlaps to some degree with better-known neo-Nazi organizations like the Base and Atomwaffen, whose members have also been prosecuted by the federal government. O9A’s followers have expressed admiration not only for Adolf Hitler but also for Islamic terrorists like Osama bin Laden, prosecutors said.

It was unclear on Monday whether Melzer had a lawyer.

Prosecutors said he enlisted in the Army in 2018 and joined O9A the next year, not long before he and his unit were deployed overseas.

Before planning the attack on his base, he steeped himself in O9A propaganda and literature published by the Islamic State, or ISIS, prosecutors said. As part of their inquiry, federal agents later found an iCloud account that Melzer used to store an ISIS document describing the murders of US military personnel, prosecutors said.

In April, after he learned that the Army planned to move his unit to a different overseas base, Melzer began to plan the assault, prosecutors said. Using Telegram, he provided members of O9A and a related group, the RapeWaffen Division, with sensitive information, including his unit’s destination, its anticipated movements and its surveillance and defensive capabilities.

In one message to O9A members, Melzer said his “military training” and “links to other groups” could be useful to them, according to the indictment. A little more than a week later, the indictment says, he sent another message in which he said he was risking his life by passing along the information and was “expecting results.”

Melzer hoped the assault, which one of his conspirators likened to a “jihadi attack,” would ignite “a new war” that would cause “mascal,” or mass casualties, the indictment quotes him as saying.

Prosecutors said he also promised to leak more information about his unit once he arrived at the new base so as “to maximize the likelihood of a successful attack.”

The top charge against Melzer — conspiring to murder U.S. nationals — carries a maximum sentence of life in prison. The other charges against him include conspiring to murder US military service members and providing material support to terrorists.

Prosecutors did not disclose how federal agents and the Army thwarted Melzer’s plot. But they said he had confessed to it almost immediately during an interview on May 30 while in custody.

Cases involving US service members who are accused of conspiring with neo-Nazis are rare, but organizations that monitor extremist activity have warned that the armed forces can be a training and recruiting ground for hate groups.

In February 2019, Christopher Hasson, a Coast Guard lieutenant and self-described white nationalist, was arrested in Maryland and charged with plotting to kill a long list of prominent journalists and Democratic politicians, as well as professors, judges and what he called “leftists in general.” He was sentenced to 13 years in prison after pleading guilty to federal gun and drug charges.