The defendants, who allegedly planned to join al Qaeda and the Taliban in Afghanistan, were arrested for plotting to bomb government facilities and public places, authorities said.
According to a federal complaint unsealed Monday during their initial appearances, Sohiel Omar Kabir, 34, introduced two California men, 23-year-old Ralph Deleon of Ontario and 21-year-old Miguel Alejandro Santana Vidriales of Upland, to the radical Islamist doctrine of Anwar al-Awlaki, a deceased al Qaeda leader.
Kabir is a former resident of Pomona and naturalized United States citizen, born in Afghanistan.
Deleon and Santana allegedly converted to Islam in 2010 and began engaging with Kabir and others online in discussions about jihad, including posting extremist content to Facebook.
According to the complaint, Santana stated that he had experience with firearms and that he wanted to become a sniper. Deleon stated he wanted to be on the front lines with a second choice of explosives. Both men also indicated they were willing to kill an enemy.
According to the FBI, Santana once told an FBI undercover agent in an online conversation that he wanted to commit jihad and expressed interest in a jihadist training camp in Jalalabad, Afghanistan.
Authorities allege Kabir traveled to Afghanistan and communicated with Santana and Deleon over the Internet so he could arrange for their travel to join him and meet with his contacts for terror organizations. They later recruited 21-year-old Arifeen David Gojali of Riverside.
Santana and Deleon were in federal custody and Gojali's detention hearing was continued to next Monday. Kabir was in custody in Afghanistan.
If convicted, the defendants each face a maximum penalty of 15 years in federal prison.
The Associated Press contributed to this report.