By Susan Guyett

INDIANAPOLIS (Reuters) - John Walker Lindh, the so-called "American Taliban" captured in Afghanistan and imprisoned in the United States after the September 11, 2001, attacks, testified in federal court on Monday that a ban on group prayer for Muslim prisoners was absurd.

Lindh joined a complaint filed by two other Muslim prisoners challenging a ban on daily group prayers at the federal prison in Terre Haute, Indiana, where he has been incarcerated since 2002. He was captured in Afghanistan during the fighting after the 2001 attacks on the World Trade Center and Pentagon.

The bearded Lindh, 31, who is serving for fighting with the Taliban in Afghanistan, wore ankle chains in the courtroom on Monday and his hands and arms were tightly bound as he was led out after two hours of testimony.

With the help of a glossary for court officials, Lindh guided the court through a series of lessons on Muslim prayer traditions.

The prison warden halted daily group prayers in 2009 and allowed them only on the holy day of Friday after some incidents among the Muslim prisoners.

Lindh said group prayers should be allowed because inmates in the facility are free to congregate for other reasons most of the day. He testified that there are no conversations or sermons during the prayer sessions and that attendees do not speak for most periods of the prayer service, which is led by an imam.

"If something is wrong you oppose it. If something is right you praise it," Lindh said. "Muslims can't be neutral. That is the course I am taking."

Lindh's parents were in the courtroom, according to ACLU of Indiana attorney Ken Falk, who is representing Lindh.

Lindh was born in the United States and his parents have said he made a mistake in going to Afghanistan, where he joined the Taliban.

The Taliban ruled Afghanistan before the September 11, 2001, attacks and allowed al-Qaeda to plan the attacks from within the country. They were overthrown by U.S.-led forces but still are fighting an insurgent war in Afghanistan.

(Editing by Greg McCune)