By Lisa Shumaker

(Reuters) - Four men have been arrested in southern California 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 said on Monday.

Other charges the men face include plotting to bomb government facilities and conspiracy to kill Americans.

Since the September 11 2001 attacks, the U.S. 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 naturalized U.S. citizen who was born in Afghanistan and served in the U.S. 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 U.S. 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". Continued...