A 21-year-old Syrian man was arrested Wednesday morning by the FBI's Joint Terrorism Task Force after allegedly plotting to bomb a Pittsburgh church next month in the name of the so-called Islamic State to “take revenge” for his terrorist “brothers.”

The plot was far enough along that the suspect, identified as Mustafa Mousab Alowemer, purchased a slew of supplies for the bomb-making, including nail polish remover, batteries, ice packs, and nails, according to the Justice Department. The target was said to be the Legacy International Worship Center on the north side of Pittsburgh, which describes itself as a multicultural, “Christ-centered” and “Bible-driven” ministry on its website.

Alowemer allegedly planned the bombing with someone he believed to be a fellow Islamic State member who was actually an undercover FBI agent. While preparing the attack for July, Alowemer described the church as “Nigerian” and “mushrikeen,” an Arabic term for those who commit idolatry, and called for using a bomb big enough to “destroy it all” in comments to the undercover agent, according to a criminal complaint.

“They are all polytheists. We, we, take revenge for our brothers in Nigeria,” Alowemer told the agent, prosecutors said.

Alowemer also allegedly discussed the possibility of targeting Yazidi families in the city, a Shia mosque, and a U.S. military member before settling on the church as a target.

For weeks, he is said to have sent ISIS propaganda to the undercover agent, along with bomb-making instructions.

Prosecutors say Alowemer planned on planting a backpack on the side of the church filled with explosives before heading to a mosque with his accomplices so they would have “witnesses to their presence at morning prayers.” He at one point also suggested leaving a second explosive device at the scene to hit first responders and had no issue with killing others in the surrounding residential neighborhood during the attack, prosecutors say.

“This operation must be done on a Sunday night in order to shock the enemies of Allah almighty everywhere and all over America,” he allegedly wrote in a set of instructions for the plot, adding that the attack would prevent Americans “from going to their churches and instill fear in their hearts.”

Prior to the conception of the bombing plot, Alowemer—who arrived in the U.S. in 2016 as a Syrian refugee—corresponded with another undercover agent and allegedly expressed his allegiance to ISIS leader Abu Bakr al-Baghdadi.

“Brother, you said you were going to talk to the brothers there about [me joining [them], what happened? By Allah my brother, I'm burning from inside for what happened to the Muslims in New Zealand,” he was quoted as writing to the agent, referring to the Christchurch mosque shooting that occurred earlier this year.

He has been charged with one count of attempting to provide material support to ISIS and two counts of distributing information relating to an explosive, destructive device in relation to the bomb plot. According to the Pittsburg Post-Gazette, he was expected to appear at a hearing in federal court on Wednesday but it was postponed until Friday.