Mychal Bell had initially been tried as an adult

Mychal Bell, 17, had been in jail since December when he and five other black pupils were accused of beating up a white boy amid racial tension in Jena.

He was the only one of the six who remained in custody.

Last week, thousands marched in the small town to denounce what they said was continuing racism in Louisiana.

Mychal Bell's release came after prosecutors said they would no longer seek to try him in an adult court, where he had faced a maximum of 15 years if found guilty.

He was found guilty of second-degree battery in June by an all-white jury before the case was overturned by an appeal court.

He still faces trial in juvenile court over the beating, meaning that, if convicted there, he may be held only until he turns 21.

Nooses

The case of the six black teenagers, who became known as the Jena Six, provoked one of the biggest civil rights protests in recent years.

Last week's rally brought people from across the US

Demonstrators criticised what they said was a double standard of prosecution for blacks and whites.

The black teenagers had been charged with attempted murder after they allegedly attacked a white pupil at their school in Jena, although these charges were subsequently reduced.

The white teenage victim was beaten unconscious and had a badly swollen face, but was able to attend a school event the same evening.

Racial tensions had been running high at the school after three nooses were found hanging from a tree in the school yard, the day after a black pupil had sat in its shade.

That incident, with echoes of lynching, resulted in three white students being suspended from school, but not prosecuted.

The district attorney, Reed Walters, said he could find no state law under which to charge them.

Four of the Jena Six, including Mychal Bell, face assault charges, one defendant has yet to be charged and the sixth teenager's case is sealed in juvenile court, according to the Associated Press news agency.