A teen from Colorado was arrested at an airport Monday for allegedly attempting to join ISIS, the Department of Justice (DOJ) reported.

Eighteen-year-old Humzah Mashkoor was arrested at Denver International Airport, with the arrest marking a development in a two-year FBI investigation into Mashkoor, according to DOJ.

Court documents reveal that Mashkoor, arrested on charges of attempting to provide material support to ISIS, planned to travel to the United Arab Emirates. His alleged final destination was Afghanistan or Syria, where he intended to serve as a fighter for the group.

The FBI’s Denver Field Office first interacted with Mashkoor on social media when he was 16. Undercover agents reportedly engaged with him online, where he used the pseudonym “Humzah Afghan.” The criminal complaint against Mashkoor details his expressed support for ISIS, including sharing execution videos and discussing his desire to work with extremist groups, ABC News reported.

Colorado teenager charged with attempting to join ISIS. https://t.co/iEnmuvYDmi

— ABC News (@ABC) December 20, 2023

Mashkoor’s statements to undercover officers highlighted a shift in his allegiances from the Taliban to ISIS, particularly following the 2021 Kabul Airport bombing. His alleged readiness to commit violent acts and his support for ISIS’s objectives were evident in his communications, according to ABC News. (RELATED: ISIS Claims Responsibility For Catholic Mass Bombing)

“Are you ready?” he allegedly wrote to an undercover FBI agent about his intended trip to Afghanistan, the outlet reported. “Once we go there’s no turning back… We leave behind everything… Our family’s [sic]… Our homes… Our friends… For the sake of Allah. … Life won’t be easy, we will be strangers moving from place to place… Hated by the whole worlds.”

His travel plans for Dec. 11 were postponed to Dec. 18, the day of his arrest, according to the outlet. This case is being prosecuted by Assistant U.S. Attorney Laura Cramer-Babycz for the District of Colorado, with assistance from Jennifer Levy of the National Security Division’s Counterterrorism Section, ABC noted.