LOS ANGELES: A 24-year-old American charged with trying to join Al Qaeda was intercepted by the FBI after using the Internet and Facebook to connect with the terrorist group, a prosecutor said Monday.

Sinh Vinh Ngo Nguyen confessed to federal agents that he had planned to offer himself as a trainer of some 30 Al Qaeda forces to ambush troops in Syria, where he had already spent five months fighting with rebels, Assistant United States (US) Attorney Judith Heinz said.

US District Judge John Walter expressed skepticism with some of the evidence and questioned whether the want-to-be terrorist had any special skills to offer Al Qaeda.

Nguyen has pleaded not guilty to two charges of making a false statement on a passport and attempting to provide material support and resources to a terrorist organisation.

Heinz said a confidential informant and an undercover FBI agent posing as an Al Qaeda recruiter gathered evidence against Nguyen after he reached out on the Internet and on his Facebook page to join the terrorist group.

He was arrested Oct 11 at a Santa Ana bus station as he prepared to board a bus for Mexico with plane tickets to Pakistan, authorities said.

The undercover agent escorted him to the bus and told him they would be meeting ''his sheikh'' in Peshawar, the prosecutor said.

When agents arrested him, Nguyen exclaimed, '''How did you guys find out?''' Heinz relayed.

The prosecutor said Nguyen had a fake passport, $1,850 in Syrian currency and a pamphlet with extensive instructions on shooting and setting up battle plans.

Three swords, two large axes, two hatchets and a copy of the famous tome, ''The Art of War,'' were found in the Garden Grove home where he lived with his parents.

Heinz said Nguyen planned to train Al Qaeda forces in shooting.

The judge noted that Nguyen was never a member of the US armed forces, having been rejected because of a hearing problem.

''I don't see evidence that this defendant had any particular skill in firearms,'' he said, ''or that he had the ability to procure or deliver weapons to these 25-30 individuals. This is the part of the case that escapes me.''

The judge was also dismissive of the prosecution's pointing out that Nguyen owned two guns and went target shooting, saying he sometimes went target shooting himself.

Nguyen made no comment during the hearing and was ordered to be held without bail.

Walter set a Dec 3 trial date and urged the government to quickly analyse the content of eight computers and four cellphones taken from Nguyen's home.

When the judge pressed Heinz for more information, she said Nguyen waived his Miranda rights shortly after his arrest, confessing within 90 minutes, then going on for 50 hours of tape recorded interviews, much of it detailing his experiences in Syria.

The Miranda rights, named after the plaintiff in a Supreme Court case, requires police to advise people in custody that they have the right to remain silent and the right to consult with an attorney before being questioned.

''He confessed on the 50 hours of interviews,'' the prosecutor said, relating Nguyen's plan to go to Pakistan, fake his own death and assume a new identity ''to be a soldier for jihad''.

Prosecutors intended to present excerpts from the interviews during trial, Heinz said, along with Facebook posts where Nguyen reportedly says he killed someone in battle during the five months he spent in Syria last year.

The FBI operative told Nguyen that getting a fake passport would be a lot easier than faking his death, and offered help.

The prosecutor said Nguyen filled out the passport request with a new name, Hasan Abu Omar Ghannoum, and gave it to the agent, who then sent it to the US government, which issued the passport.

The judge then asked Heinz again to identify the resources Nguyen was providing to Al Qaeda.

''He was providing himself,'' she said.