But 22-year-old Cole Bridges was actually communicating with an FBI employee posing as a supporter of the violent extremist organization, which once held swathes of Iraq and Syria before losing the territory it seized to local forces backed by a US-led international coalition.

Bridges on Wednesday "pleaded guilty to attempting to provide material support to a designated foreign terrorist organization and attempting to murder US military service members," the Justice Department said in a statement.

The department said the private first class -- who joined the US Army in 2019 -- went from consuming online jihadist propaganda to trying to provide information to aid IS.

Bridges began communicating with the FBI employee in October 2020 and "provided training and guidance to purported (IS) fighters who were planning attacks, including advice about potential targets in New York City."

He later told the alleged IS supporter how the jihadists could best attack American forces in the Middle East, diagramming maneuvers for them to "maximize the lethality of attacks" and giving advice on how to fortify an encampment against a special forces attack.

He then sent a video to the FBI employee of himself in body armor standing in front of a flag used by IS fighters, and followed it with a second clip in which he "narrated a propaganda speech in support of the anticipated ambush by (IS) on US troops," the Justice Department said.

After the jihadists lost their last scraps of territory to local Kurdish-led forces in 2019, IS remnants in Syria mostly retreated into desert hideouts in the country's east, and are periodically targeted by US raids and strikes.

Bridges will be sentenced on November 2, with the two charges he pleaded guilty to each carrying a maximum of 20 years in prison.