Four men with ties to Southern California have been arrested and charged with plotting to kill Americans overseas by joining up with al Qaeda to engage in "violent jihad" or Islamic holy war, the FBI says.
Other charges the men face include plotting to bomb government facilities and conspiracy to kill Americans.
Since the September 11, 2001, attacks, the US government has stepped up surveillance efforts to catch both domestic and foreign militants, but has repeatedly warned that such groups continue to pose a threat.
The authorities said Sohiel Omar Kabir, 34, traveled to Afghanistan where he planned to introduce the other suspects to his al Qaeda contacts.
Kabir is a naturalised US citizen who was born in Afghanistan, and served in the US Air Force from 2000 to 2001.
Also arrested were Ralph Deleon, 23, of Ontario, California; Miguel Alejandro Santana Vidriales, 21, of Upland; and Arifeen David Gojali, 21, of Riverside. If convicted, the men face up to 15 years in prison.
The FBI said in its complaint that Kabir had introduced Deleon and Santana to radical Islamic teachings in 2010, including those of al Qaeda leader Anwar al-Awlaki, who was killed by a US drone. Deleon and Santana then converted to Islam.
In one conversation with an FBI confidential source, Santana and Deleon discussed their preferred roles when it came to carrying out attacks.
Santana stated that he had experience with firearms and that he wanted to become a sniper, while Deleon said he wanted to be on the front line but that his second choice was handling explosives.
Both men also indicated they were willing to kill people they perceived to be enemies. When asked if he had thought about how it would feel to kill someone, Santana told the informant: "The more I think about it, the more it excites me".
Deleon is a lawful permanent resident alien who was born in the Philippines, and Santana is a lawful permanent resident who was born in Mexico and had applied to become a US citizen, according to the FBI.
In September 2012, Deleon and Santana recruited Gojali, a US citizen. The three men planned to travel overseas for training and to carry out attacks in Afghanistan or Yemen.
In preparation for their trip, the FBI said the men had removed all radical Islamic postings from their Facebook accounts. Deleon and Santana also worked out and practiced shooting assault rifles at a Los Angeles firing range.
Just last week, the three men sold personal belongings, including Deleon's car, and bought airline tickets to travel from Mexico City to Istanbul, Turkey, on November 18.
They then planned to make their way to Kabul, Afghanistan, the FBI said.
Santana, Deleon and Gojali were arrested on Friday and made their initial court appearance later in the day in US District Court in Riverside, California, where they were ordered to remain in federal custody.
Gojali's detention hearing was continued to November 26. Kabir was taken into custody on Saturday in Afghanistan, the FBI said.