The FBI says it has foiled an attack on the Mall of America perpetrated by a teenager with an assault rifle.

MINNEAPOLIS– The FBI foiled an attack on the Mall of America by a teenager after agents provided him with an assault rifle, authorities said Wednesday.

The 18-year-old man had been under investigation for nearly two years, exchanging messages with a confidential informant, before agents sold him the rifle and ammunition, according to a federal complaint outlined by U.S. Attorney Daniel Rosen.

Sheikhdoon Abdullahi Mohamud, 18, was arrested Tuesday in a public park after paying $600 to an undercover FBI employee posing as an ISIS member for an AK-47 and 200 rounds of ammunition, according to the criminal complaint.

In text messages sent to a confidential FBI source, Mohamud repeatedly asserted his intention to carry out an attack aimed at killing non-Muslims, according to the complaint. It was not immediately known whether the teen had an attorney who could speak on his behalf.