The U.S. military said Friday that it had designated 14 captives at the Guantánamo detention center as “hunger strikers,” and that six of them were being force-fed through tubes in the first admission of a protest claimed by defense attorneys.

The acknowledgement came a day after 51 attorneys wrote Secretary of Defense Chuck Hagel of their “urgent and grave concern about a mass hunger strike taking place at the prison, now in its second month.” They sought Hagel’s intervention in “a serious threat to the health and life of detainees.”

Navy Capt. Robert Durand, the prison spokesman, denied “a widespread phenomenon, as alleged.” But he said, for the first time after weeks of denial, that the number had surged to 14 from the five or six detainees who had for years been consider hunger strikers among the 166 captives at Guantánamo.

One captive was in the prison hospital Friday, Durand said. Five others were being fed elsewhere through tubes tethered through their noses into their stomachs. And eight other captives had not yet been sufficiently malnourished to merit tube feedings but had shunned enough consecutive meals and lost enough weight to meet the Pentagon’s Guantánamo definition of a hunger striker.

Lawyers and the military have for more than a week exchanged angry denunciations over what is clearly a period of increased tension in the prison camps. Durand accused the lawyers of spreading “outright falsehoods and gross exaggerations,” notably allegations that prison staff had been mistreating the captives’ Qurans to the point of desecration.

Lawyers for the captives accused the prison of covering up events that signaled the desperate situation in the camps — from a guard’s decision to fire a first-ever round of rubber pellets into a recreation yard for compliant captives, to a request by some captives to turn their copies of the Quran back in to the prison commander on grounds they couldn’t protect them.

Reports of detainees withering away have trickled out because of a security regime that prohibits defense attorneys from describing what their captives clients tell them until after their notes pass through a security review that can take weeks.

Uniformed military defense lawyers for some captives are exempt from the security review. In one such instance, Army Capt. Jason Wright described his alarm this week at seeing an already slim Afghan client, Obaydullah, about 30, who said he’d been subsisting for weeks on water or honey water.

“I was shocked. He’s lost at least 15 pounds,” said Wright. “He told me that detainees were passing out almost by the day. He conveyed that a detainee recently fell down and was in need of medical attention and it took several minutes for the other detainees to actually flag down a guard” and take the collapsed captive to the medical center.

Durand, the prison camps spokesman, won’t speak to a specific captive’s case. So it was not possible to know if Obaydullah was on the list Friday of the 14 hunger strikers.

But the military at Guantánamo argues that, in the cooperative prison that holds about 100 captives, those who tell their lawyers they are hunger strikers and are refusing regular meals are actually snacking from pantries or other supplies of food in the Camp 6 cellblocks.