A North Carolina teenager was charged with plotting to kill Americans on behalf of the Islamic State after he was turned in to the police by his own father.

Justin Sullivan, 19, was reportedly in contact with an undercover FBI agent this month, claiming he was a Muslim convert who saw himself as a "mujahid." Authorities started observing the younger Sullivan after his father, a retired marine, requested for it, according to Christian News.

In the complaint filed with a federal court, Sullivan was quoted as saying that "the war is here" and invited the agent to join the "Islamic State of North America."

He told the agent he planned to carry out "minor assassinations" in the US "before the big attack for training." He said he would "send a video [of the attack] to ISIS."

He also revealed that he planned to buy a semi-automatic AR-15 rifle at the Hickory Gun Show to be used for the mass killing. He said he also intended to use bombs and chemical weapons.

The teenager asked the agent his thoughts about making a homemade silencer, saying he had to assemble it within a week. He also asked the agent to murder his parents in exchange for payment.

Sullivan's parents called 911 about their son's unusual behaviour.

"I don't know if it is ISIS or what, but he is destroying Buddhas and figurines and stuff," his father, Rich Sullivan, said during the call. "I mean, we are scared to leave the house."

A neighbour also said he saw the teenager practising with a gun before the police arrived to arrest him on Friday.

"[W]hen I was getting the grill ready, I heard gunfire from what sounded like a high-calibre pistol—five or six shots," the neighbour said. "He emptied whatever he had."

Sullivan is now facing one count of trying to provide material support to a terrorist group. He is also charged with two counts of transporting and receiving a silencer with intent to commit a felony.

"As alleged in the complaint, the defendant was planning assassinations and violent attacks in the United States and is charged with attempting to provide material support to [ISIS] and federal firearms violations," Assistant Attorney General John Carlin said in a statement.

"The National Security Division's highest priority is counterterrorism and we will continue to pursue justice against those who seek to provide material support to designated foreign terrorist organisations."

Sullivan's arrest increases the number of Americans charged this year with supporting ISIS to almost 30. Many of those arrested are teens and young adults like him.

"These were not confused young men," Minnesota US Attorney Andrew Luger told reporters. "These are focused young men who were intent on joining a terrorist organisation by any means possible."

At his first court appearance, Sullivan was "wide-eyed, seemed a little confused, uncomfortable about where he was," according to ABS-CBN.

Sullivan's mother was described by reports as Filipino.