WASHINGTON: The FBI has arrested an 18-year-old man who had been plotting to carry out a mass shooting at the Mall of America near Minneapolis in the name of ISIS, according to court filings.

He was arrested on Tuesday after an FBI undercover agent sold the Minnesota man, Sheikhdoon Abdullahi Mohamud, an AK-47, ammunition and magazines for US$600, according to the complaint. Mohamud told the informant he planned to use the items to kill 30 to 60 people at an event at the mall in late October.

Mohamud was charged with one count of knowingly receiving a firearm and ammunition in order to commit an act of terrorism. His lawyer did not immediately respond to a request for comment.

According to the complaint, Mohamud told an FBI source on various messaging platforms that he intended to travel overseas to fight on behalf of al-Shabaab, a designated foreign terrorist organisation. He said if he couldn't travel, he planned to conduct a mass shooting. He later said he wanted to join ISIS.