WASHINGTON (AFP) – A 20-year-old US national has been arrested and charged with trying to join Somalia's Shebab militants, the latest in a slew of homegrown extremism cases in the United States.

Zachary Adam Chesser, 20, was charged Wednesday in a criminal complaint that he provided material support to Shebab, a designated foreign terrorist organization, the Justice Department said.

Officials said Chesser sought to use his infant son as cover so no one would suspect he was traveling to Africa to join the Shebab, which earlier this month claimed suicide bombings that killed 76 people in Uganda.

According to court documents, Chesser also was linked to a website that called for protests against the creators of satirical cartoon "South Park" for the show's depiction of the Prophet Mohammed earlier this year.

First interviewed by the FBI in May 2009 about jihadist Internet postings, Chesser was under surveillance when he tried to board a flight to Uganda with his son on July 10 at New York's JFK airport.

Denied check-in and told he was on a no-fly list, the suspect was allowed to remain at large until his arrest on Wednesday.

"This case exposes the disturbing reality that extreme radicalization can happen anywhere, including Northern Virginia," said US Attorney Neil MacBride.

"This young man is accused of seeking to join the Shebab, a brutal terrorist organization with ties to Al-Qaeda. These allegations underscore the need for continued vigilance against homegrown terror threats."

In interviews with FBI agent Paula Menges in the days leading up to his arrest, he poured out a stream of valuable information about how the Shebab recruits and trains its foreign fighters, the charge sheet said.

Chesser portrayed the Shebab as a decentralized entity with smaller autonomous units carrying out missions independently, adding that it was much easier to join than other groups in Afghanistan and Iraq.

"He said that he had been in contact with people from the Shebab, and that he would have no problem in getting into the Shebab when he reached Somalia," the court filing said.

"Chesser told Menges that training camps for the Shebab will begin after Ramadan (in approximately two months), and Chesser was hoping to get there in enough time to be prepared for this start date," the indictment said.

"Chesser said that the initial training, which includes basic training and firearms, is about six weeks long. Additional training would occur if someone were to obtain a special skill, such as bomb making or sniper qualifications."

The Shebab was telling recruits to bring laptops for the fighters and cameras to produce quality propaganda videos, the court documents said.

Chesser said he would likely be recruited as a "foreign fighter" and placed with the media branch in Mogadishu, Somalia, where he would still get to serve on the "front line."

The charge sheet detailed several earlier interviews of Chesser by Menges in May and June 2009 in which he was quizzed about his numerous postings on jihadist forums, many under the name Abu Talhah Al-Amrikee.

In one interview, he admitted to being in email contact with Anwar al-Awlaki, the radical Muslim cleric suspected of being a key leader of Al-Qaeda in the Arabian Peninsula and links to other homegrown US extremists.

A search of Chesser's house in June uncovered a journal in which he stated his intention to join the Shebab and detailed an earlier failed bid to reach Somalia, in November, via Kenya.

Following a spate of attacks or near misses -- at the Fort Hood military base last year and in Times Square, New York in May -- President Barack Obama's administration has had to refocus national security on homegrown extremists.

"We can't fight terrorists alone," FBI assistant director Shawn Henry said in a statement on Wednesday on Chesser's arrest.

"Religious leaders of all faiths, family members and particularly the younger members of our communities need to speak up and speak out against individuals who participate in actions like those alleged here."