MIAMI – The U.S. military said Friday that it had designated 14 captives at the Guantanamo 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.”

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 considered hunger strikers among the 166 captives at Guantanamo.

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 Guantanamo definition of a hunger striker.