Conor Climo, 23, was arraigned in federal court in the western US state of Nevada after FBI agents monitored his online conversations with a "white supremacist extremist organization" committed to pursuing its goals "via terrorism and other violent acts," the US attorney's office said in a statement.
They discussed making explosives and targeting the synagogue as well as conducting surveillance on a gay bar, the criminal complaint said.
Climo was arrested on Thursday. Authorities seized a notebook with hand-drawn plans for a potential attack in the Las Vegas area and drawings of timed explosive devices.
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"Threats of violence motivated by hate and intended to intimidate or coerce our faith-based and LGBTQ communities have no place in this Country," said federal prosecutor Nicholas Trutanich.
"Law enforcement in Nevada remains determined to use the full weight of our investigative resources to prevent bias-motivated violence before it happens."
If convicted, Climo faces a maximum penalty of 10 years in prison and a $250,000 fine.
Members of the organization he communicated with "believe in the superiority of the white race," and the group encourages attacks on the federal government, as well as minorities and LGBTQ people, the statement said.
Climo's arrest comes after three mass shootings in the US in the past two weeks.
Last weekend, a young white man shot and killed 22 people at a Walmart store in El Paso, Texas, a city with a population that is 83 per cent of Hispanic descent.
In a manifesto posted online before the attack, the shooter said he was fighting back against a "Hispanic invasion" of Texas.
FBI special agent Aaron Rouse said, "the FBI will always be proactive to combat threats that cross a line from free speech to potential violence."
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