Authorities in Southern California were able to disrupt an alleged terrorism plot aimed at "multiple targets" in the Southland the Department of Justice said today.

Mark Steven Domingo, 26, of Reseda, California, was arrested and is facing federal charges in connection with a terrorist plot in which he planned on detonating an improvised explosive device (IED) to cause a mass casualty incident, the Department of Justice said in a news release Monday afternoon.

Federal prosecutors say the former U.S. Army Infantryman “planned and took steps to manufacture and use a weapon of mass destruction in order to commit mass murder.”

"This investigation successfully disrupted a very real threat posed by a trained combat soldier who repeatedly stated he wanted to cause the maximum number of casualties," said United States Attorney Nick Hanna. "Protecting Americans from terror attacks is the number one priority of the Justice Department, and anyone who plots to use a weapon of mass destruction will be held to account."

Domingo first came to law enforcement's attention after he logged onto an online message board and began posting incendiary comments in support of a violent jihad and desire to seek retribution for attacks against Muslims, the affidavit states. After considering attacks against Jews, churches or police officers, prosecutors say Domingo planned to detonate an IED scheduled to take place in Long Beach over the weekend.

The suspect reportedly asked undercover FBI agents to help him find a bomb-maker, and Domingo purchased several hundred nails to be used as shrapnel inside the IED. He "specifically bought three-inch nails because they would be long enough to penetrate the human body and puncture internal organs,” the affidavit states. He asked the bomb-maker to create an IED that could cause up to 50 casualties and referenced the Boston Marathon bombing.