LOS ANGELES — Federal prosecutors charged a 26-year-old U.S. Army veteran who they say expressed support for the Islamic State with plotting to bomb a local white nationalists rally. They say he also considered targeting churches, military facilities, police and Jewish holiday gatherings.

In a 30-page complaint unsealed Monday, federal prosecutors offered a detailed account of a government sting operation in which Mark Steven Domingo allegedly told FBI informants of his desire for a mass-casualty event on the scale of the 2017 Las Vegas shooting massacre and 2013 Boston Marathon bombing in retribution for last month's attacks on two New Zealand mosques that left nearly 50 dead.

Domingo, whose military service included combat in Afghanistan, was arrested Friday night by FBI agents after they said he conducted surveillance of his intended target, a public park in Long Beach. He was accompanied by two others who he thought were to be accomplices in the attack but who are actually an undercover FBI agent and informant who helped make the case against him.

Domingo, who lives in Reseda, California, is charged with providing and attempting to provide material support to terrorists. Prosecutors said that Domingo had provided boxes of nails he believed were to be used in the construction of a bomb. The device had been rendered inert by the FBI before it was delivered to Domingo.

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“At no time was the public in danger and there is currently no known threat to public safety," Los Angeles FBI chief Paul Delacourt said.

At Domingo‘s first court appearance Monday afternoon, U.S. Magistrate Judge Paul Abrams set arraignment for May 31 and denied bail, saying there was ample proof that Domingo represented a threat to the community.

Assistant U.S. Attorney Reema Mohamed El-Amamy argued that not only did Domingo’s weapons and threats represent a danger, but that he had been plotting to kill a neighbor to see how long it took for the police to arrive.

His public defender, David Israel Wasserman, said Domingo has strong ties to the community, including many relatives, and did not carry through on any of the purported threats. He also pointed out that Domingo has no criminal history.

Domingo's arrest comes as Southern California reeled from a weekend attack on a San Diego-area synagogue in which one woman was fatally shot during a service on the last day of Passover. Police arrested a 19-year-old suspect in the synagogue shooting who allegedly spoke of a desire to kill Jews prior to the Saturday attack.

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In Los Angeles, U.S. Attorney Nick Hanna characterized Domingo as "a very real threat" despite the FBI's close surveillance and under-cover contacts with him.

"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,” Hanna said. "Anyone who plots to use a weapon of mass destruction will be held to account.”

Federal investigators began tracking Domingo in early March, according to court documents, after he posted messages online describing his support for "violent jihad and his aspiration to conduct an attack in the Los Angeles area."

"America needs another vegas...something to kickoff civil unrest," Domingo allegedly wrote in a rambling ungrammatical March 3 post, referring to the 2017 Las Vegas shooting that left 59 dead. "Its not about winning the civil war its about weakening america giving them a taste of the terror they gladly spread all over the world."

Eleven days later, Domingo angrily responded to the New Zealand mosque shooting, declaring: "there must be retribution."

Domingo's communications prompted the FBI to direct a longtime informant to make contact with him. They met in mid-March to discuss possible targets. During that first meeting with the informant, who has been paid more than $300,000 for his work for the FBI since 2013, Domingo allegedly shared his desire to attack a range of people and locations, including "Jews, police officers, churches and a military facility."

That evening, after dinner and a prayer service, the two allegedly went on a drive and discussed tactics and cased possible targets, including a National Guard Armory and a Jewish neighborhood.

"This is the business street," Domingo allegedly told the informant, whom the government did not identify. "The (Jews) come here on Saturday. They're all up and down the street, but there's cameras everywhere."

The discussions, according to court documents, went on for weeks with the informant discussing possible sources for explosives while pressing Domingo for his commitment to proceed with an attack.

At one point, Domingo discussed a possible assault on the iconic Santa Monica Pier before settling on the Sunday rally in Long Beach. "Domingo said they should try to find the most crowded areas in order to kill the most people in the attack," the court documents state.

He was arrested while transferring one of the inert devices into to an undercover agent's vehicle.

"Thank God this didn’t work out, because at the end of the day, it’s about blood being spilled,” Long Beach Police Chief Robert Luna said.

Michael McGarrity, assistant director of the FBI's counter-terrorism section, said Domingo "moved very quickly from talking about violence to mobilizing to commit such an attack."

“This case should remind the public of the need to be vigilant and notify law enforcement if you see suspicious behavior.”

Johnson reported from Washington.