An 18-year-old Minnesota man who allegedly pledged allegiance to ISIS and discussed carrying out a mass shooting at the Mall of America was arrested after buying an AK-47-style rifle, magazines and ammunition from an undercover FBI employee, according to newly filed federal court documents.

Sheikhdoon Abdullahi Mohamud had allegedly spent months discussing his desire to carry out an attack, telling an FBI confidential source in September, "I can’t wait until I kill kuffar man. October 24 is the day insha Allah," according to an affidavit filed in federal court in Minnesota.

When the source later asked why he had chosen Oct. 24, Mohamud allegedly pointed to a "Hmong Arts Celebration" at the Mall of America, saying it would have "a lot of people," the affidavit states.

"Muhammad met with someone he believed to be a loyal member of ISIS to attempt to purchase an AK-47 rifle, knowing it would be used in a felony or federal crime of terrorism," Special Agent in Charge, FBI Minneapolis Field Office, Christopher Dotson said at a press conference Wednesday. "Mohammed planned to use the gun he bought in a high-traffic public area just a few weeks' time in support of a designated foreign terrorist organization."

Mohamud is now charged with knowingly receiving a firearm and ammunition while knowing or having reasonable cause to believe they would be used to commit a felony and federal crime of terrorism.

Mohamud, who was born in the United States and is a U.S. citizen, is the son of Somali nationals who later became naturalized U.S. citizens, multiple federal law enforcement sources told Fox News Digital.

His parents arrived in the U.S. through a New York City airport in 2000, according to the sources, though it remains unclear whether they entered on visas or as refugees. His mother became a naturalized citizen in 2010 and his father in 2017.

FBI Director Kash Patel told Fox News Digital in a statement that the suspect "allegedly obtained a weapon he hoped to use in a mass casualty attack in support of ISIS, but this FBI arrested him and put a stop to his plans."

"Once again, this FBI is moving more effectively than we ever have before at stopping terrorists before they can attack Americans – with over 1,100 individuals prevented from conducting attacks, over 4,000 foreign terrorist organization related disruptions and arrests, a 38% increase, and more," Patel said. "We will continue to use every resource we have to detect and prevent acts of terrorism and wipe out their networks all over the country. Thank you to FBI Minneapolis, who did an outstanding job in the investigation and likely saved lives."

President Donald Trump also praised the FBI’s handling of the case while speaking to reporters Wednesday.

"I did hear about it. And they did a great job. The FBI did a great job," Trump said.

Mohamud appeared before a federal judge in Minnesota on Wednesday for an eight-minute initial hearing, according to federal court records.

U.S. Magistrate Judge Elizabeth Cowan Wright ordered Mohamud temporarily detained. He is scheduled to return to court Monday, Oct. 19, at 11 a.m. ET for a preliminary and detention hearing.

Minnesota Gov. Tim Walz thanked law enforcement for acting quickly to stop the alleged plot, saying federal authorities should remain focused on preventing similar threats.

"Grateful for the swift and professional action to keep Minnesotans safe," Walz wrote in an X post. "This is exactly the kind of threat we need federal law enforcement working to prevent, and the kind of work that should remain a priority as we navigate a more dangerous world."

Mall of America said the news was unsettling for its guests, tenants, employees and the broader community while thanking the FBI and other law enforcement agencies for disrupting the alleged threat.

"We are grateful to the FBI and its law enforcement partners for their vigilance and extraordinary investigative work in identifying, disrupting and removing this threat and protecting the community we all share," Mall of America said in a statement shared with Fox News Digital.

The mall added that safety and security remain its highest priority and said it would continue working closely with local, state and federal law enforcement.

The arrest capped an FBI investigation that began around December 2024 and eventually involved a confidential human source who communicated extensively with Mohamud over encrypted messaging and social media platforms, according to investigators.

Those conversations initially centered on Mohamud allegedly wanting to leave the United States and join al-Shabaab, the Somalia-based terrorist organization. In May, he allegedly told the source he was "so excited to make hijrah" and wanted to go to Somalia, get married and "fight the enemies of Allah." He said he planned to work for about six weeks to save $2,000 for a plane ticket, according to the affidavit.

By July, however, investigators say his plans had changed.

Mohamud allegedly told the source he did not have enough money to travel to Somalia and wrote, "so i will do attack here." He later discussed buying two pistols online and going to the Mall of America or the Minnesota State Fair around Christmas, according to the affidavit.

Mohamud allegedly discussed attacking the Mall of America with an assault rifle and told the source he could "drive straight to the crowded place and start shooting." In September, investigators say he also sent the source a selfie-style video pledging allegiance to ISIS and its leader.

The FBI then arranged an undercover weapons transaction. On Sept. 25, the source told Mohamud a "brother" could sell him an AK-style rifle, magazines and ammunition, and Mohamud allegedly indicated he wanted the weapon to be fully automatic.

On Tuesday, Mohamud met the supposed ISIS-connected "brother" — actually an undercover FBI employee — and allegedly paid $600 for an AK-47-style rifle, four magazines and roughly 200 rounds of ammunition. The rifle had been rendered inoperable, though the ammunition was live. During the meeting, Mohamud allegedly said he planned to carry out a shooting at a "kuffar festival" at the Mall of America.

Mohamud left the vehicle with the rifle, magazines and ammunition in a duffel bag and was arrested at gunpoint by FBI agents, according to the affidavit.