Updated

American-born Taliban fighter John Walker Lindh testified Monday that the U.S. government is forcing him to sin by denying him the right to pray daily with other Muslims in the highly restricted federal prison unit where he is detained.

Lindh testified in federal court in Indianapolis that the Terre Haute prison where he's serving a 20-year sentence for aiding Afghanistan's Taliban government before its overthrow allows prisoners to eat, talk, play cards and exercise together, but bans daily group prayer. He contends this violates a 1993 law barring the government from curtailing inmates' religious expression without showing it has a compelling interest.

Lindh, 31, adheres to a school of Islam that requires group prayer five times a day, if possible. His testimony came at the beginning of his civil trial seeking to overturn the prison policy.

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

The government maintains that preserving security in the Communications Management Unit, where inmates' contact with the outside world is sharply restricted and most of their movements are monitored, gives it the right to limit group activities, including prayer. Group religious activities in the unit are limited to once a week for all faiths, it says.

The self-contained unit houses 43 inmates, 24 of whom are Muslim. Inmates are under open and covert audio and video surveillance, and except for talks with their attorney, all of their phone calls are monitored. Prisoners aren't allowed to touch family members during tightly controlled visits, and they must speak English unless they are reciting ritual prayers in Arabic.

Without such tight security, the government claims, the prisoners would be able to conspire with outsiders to commit terrorist or criminal acts.

Muslims in the unit are allowed to pray together only once a week, except during Ramadan. At other times, they must pray in their individual cells.

Lindh argues that the current setup doesn't meet his religious requirements, and he contends he is suing because his religion requires him to oppose injustice.

He also challenged the government's contention that allowing prisoners to pray in a group would constitute a security risk, pointing out that prisoners are allowed to engage in other activities together.

"There are no legitimate security risks by allowing us to pray in congregations," said Lindh, who wore an olive green prison uniform and a white prayer cap. "It's absolutely absurd."

The lawsuit was originally filed in 2009 by two Muslim inmates in the unit. Lindh joined the lawsuit in 2010, and the case has drawn far more attention since then. The other plaintiffs have dropped out as they were released from prison or transferred to other units.

Lindh had been charged with conspiring to kill Americans and support terrorists, but those charges were dropped in a plea agreement. He is serving a 20-year sentence for supplying services to the now-defunct Taliban government of Afghanistan and carrying explosives for them and is eligible for release in 2019.