A once-secret Guantánamo cellblock now used to punish captives was built in November 2007 for $690,000 from a crude, then 5-year-old temporary prison camp design.

Navy Cmdr. Tamsen Reese confirmed the existence of the block earlier this month, and released a photo of one steel-walled cell after detainee defenders called conditions inhumane.

It’s called Camp Five-Echo, and “serves as a disciplinary block for those non-compliant detainees in Camps 5 and 6,” Reese said in an email Friday that for the first time revealed the cost of the 4-year-old prison camps construction project.

Fewer than 150 of Guantánamo’s 171 captives are kept in Camps 5 and 6, which are steel and cement penitentiary-style copies of U.S. prisons. Former CIA prisoners are held elsewhere at a secret site at the remote Navy base, Camp 7, a jail whose price tag the Pentagon won’t reveal.

As for Five-Echo, it’s a separate 24-unit boxcar-style cellblock on the grounds of Camp 5. Its design comes from the detention center’s earliest days, 2002, when contract laborers welded cellblocks from old shipping containers.

But there’s a key difference: In the original design, the cells had a see-through metal mesh that allowed captives to communicate with and see others. For “the disciplinary block,” the military had workers weld in steel walls, sealing off each cell from the other.

The punishment block is pointedly left off the guided tour the U.S. military gives reporters. Reese, the prison camps spokeswoman, said it was first built in November 2007 and is used as a place where captives who don’t cooperate with their captors lose “privileges, and not by use of isolation or solitary confinement.”

Saudi-born Shaker Aamer, 45, a British resident, has been held there more than 100 days, said attorney Ramzi Kassem said Saturday, characterizing his client’s detention circumstances “reminiscent of Guantánamo circa 2003.”

Aamer is not able to see other captives, can only talk to them by shouting thorough his cellblock’s metal walls and is taken to an empty recreation yard to exercise alone, Kassem said.

“In Shaker’s case it’s prolonged solitary confinement. The conditions are cruel,” he said, adding that Aamer weighed 208 pounds when he was moved to the punishment block in July. He then went on a hunger strike to protest the place, and was down to 160 pounds during their last visit on Oct. 24.

Kassem said his client was put there not because of specific behavior but because he had been profiled by prison camp management as a troublemaker, “too charismatic” to be with other medium-security detainees.

It is not known when the prison commanders had the cells sealed up.

Navy Vice Adm. Patrick Walsh, investigating the camps for Geneva Conventions compliance in February 2009, described it as “an open air facility with 24 individual adjoining steel mesh cells arranged in two parallel and equal rows.” Detainees were first housed there in April 2008, he said.

A cellblock shown by a U.S. Navy photographer wielding a wide-angled lens in an open doorway has a metal bunk and faucet affixed to the wall above a squat toilet in the floor. The original box-car-style cells back in 2003 had sinks, not faucets protruding from the wall.