MIAMI (AFP) - A 16-year-old American accused of planning to join the Islamic State in Iraq and Syria (ISIS) group has been found guilty of illegal possession of a firearm in South Carolina, a prosecutor said Wednesday.

The teenager, who has not been identified because he is a minor, conspired with another person to travel to the Middle East with the intention of joining ISIS and "perhaps cause trouble in the United States," prosecutor Kevin Brackett alleged.

Because South Carolina does not have anti-terrorism laws, the youth was convicted on Tuesday of illegal possession of a handgun, an offence punishable by up to five years in prison, Brackett said.

"He was seduced by the ideology of ISIS," the prosecutor told AFP.

"I don't know specifically that ISIS reached out to him personally. But he was in contact with people in North Carolina who shared his views and he had embraced this sort of radical Islamic ideology and he wanted to travel to the Middle East to join ISIS and join that cause," he said.

During the Tuesday hearing in the town of York, Brackett alleged that the youth wanted to use the handgun to shoot US military personnel.

The youth, who was arrested in February, apologised to the court for his actions and said he did not intend to carry out his plans.

"I just regret it," he said, adding he wanted "to go back to school, I want to change everything I did."

Audio of his comments were posted on the website of The Herald, a local newspaper.

His conviction followed the arrest of six Somali Americans from Minnesota who allegedly planned to travel to Syria to join ISIS.

They were charged on Monday with conspiring to support a terrorist organisation.