Image caption John Walker Lindh was captured in Afghanistan in November 2001

American-born Taliban fighter John Walker Lindh has testified in a federal court that restrictions on group prayer for Muslim prisoners are "absurd".

Lindh has joined a legal challenge filed by two other Muslim prisoners to a ban on daily group prayers at the federal prison in Terre Haute, Indiana.

The 31-year-old is one of 24 Muslim inmates at the facility.

He is serving a 20-year sentence for aiding the Taliban after his capture in Afghanistan in November 2001.

The prison warden banned group prayers - except on Friday and during the holy month of Ramadan - after Muslim prisoners engaged in prayer allegedly ignored a fire alarm in 2007.

'A sin'

Gatherings by other faiths have also been limited at the Communications Management Unit, which opened in 2006.

I don't recognise any law but the Sharia of Islam - there is no compromise John Walker Lindh

Lindh, who was dubbed the American Taliban by media, testified on Monday in a US district court in Indianapolis that the policy was violating his right to religious expression.

Wearing a prison uniform and a white prayer cap, he said his school of Islam requires group prayer up to five times a day.

"I believe it's obligatory," he said. "If you're required to do it in congregation and you don't, then that's a sin."

He added: "There are no legitimate security risks by allowing us to pray in congregations. It's absolutely absurd."

Father's pride

The government alleges in court documents that in February, Lindh delivered a radical sermon in Arabic to other Muslim prisoners.

Media playback is unsupported on your device Media caption John Lindh's father wants presidential clemency for his son

Lindh, who converted to Islam as a teenager, was defiant when a government lawyer asked him why he had not stood as the judge entered the courtroom.

"It's against my religion," said Lindh, who was in ankle chains and had his arms tightly bound. "This procedure of standing up for people is unacceptable."

He told government lawyers: "I don't recognise any law but the Sharia of Islam. There is no compromise."

His father, Frank Lindh, who was reportedly in court, told ABC News that he was "really proud" of his son.

"It was a really well informed testimony," said Mr Lindh. "It shows how much depth of knowledge he has about Islam."