Guantanamo Bay Naval Base, Cuba ? Twice a day at the U.S. military prison here, Abdul Rahman Shalabi and Zaid Salim Zuhair Ahmed are strapped down in padded restraint chairs and flexible yellow tubes are inserted through their noses and throats. Milky nutritional supplements, mixed with water and olive oil to add calories and ease constipation, pour into their stomachs.

A Guantanamo detainee sits alone inside a fenced area during his daily outside period, at Guantanamo Bay U.S. Naval Base, Cuba. Twice a day at the U.S. military prison here, detainees Abdul Rahman Shalabi and Zaid Salim Zuhair Ahmed, who have refused to eat for nearly two years, are strapped to restraint chairs and force-fed to keep them alive.

Shalabi, 32, an accused al-Qaida militant who was among the first prisoners taken to Guantanamo, and Ahmed, about 34, have refused to eat for almost two years to protest their conditions and open-ended confinement. In recent months, the number of hunger strikers has grown to two dozen, and the military is using force-feeding to keep them from starving.

An Associated Press investigation reveals the most complete picture yet of a test of wills that’s taking place out of public view and shows no sign of ending, despite international outrage.

The restraint chair was a practice borrowed from U.S. civilian prisons in January 2006. Prisoners are strapped down and monitored to prevent vomiting until the supplements are digested.

The British human rights group Reprieve labeled the process “intentionally brutal” and Shalabi, according to his lawyer’s notes, said it is painful, “something you can’t imagine. For two years, me and Ahmed have been treated like animals.”

The government says force-feeding detainees in the restraint chair was not meant to break the hunger strikes, but it had that effect. A mass protest that began in August 2005 and reached a peak of 131 detainees dwindled at one point to just two – Shalabi and Ahmed. In recent months, though, the number has grown again.

The military won’t identify strikers, citing privacy rules and a desire to keep detainees from becoming martyrs.

But the AP was able to identify Shalabi and Ahmed, both Saudi Arabians, through interviews with several detainee lawyers and detailed military charts, obtained through the Freedom of Information Act, tracking the weights of each detainee.

Shalabi told his lawyer that other strikers include Sami al-Hajj, a Sudanese cameraman for Al-Jazeera, the Qatar-based Arabic-language TV station; Shaker Aamer, a Saudi who has acted as a camp leader; and Ghassan Abdullah al-Sharbi, a U.S.-educated Saudi engineer who told his captors he was proud to fight the U.S. and would consider it an honor to be given a life sentence.

“I don’t quite see what they have gained from it,” detention center commander Navy Rear Adm. Mark Buzby told the AP. “They are alive and healthy and we are going to keep them that way as long as they are here.”

The military counted 24 men on hunger strike this week, including 23 receiving “enteral feeding” through tubes. It begins daily monitoring and considers force-feeding any detainee who misses nine consecutive meals. All are now at 100 percent of their ideal body weight because of the tube feedings, the military says.

“We never allow them to become seriously, medically compromised,” said Navy Capt. Ronald Sollock, a doctor who commanded the detention center hospital from January 2006 until this month.

Guantanamo officials who deal directly with the strikers – and cannot be identified under military rules – cast doubt on their commitment. They say some were coerced by other detainees to stop eating and others eat McDonald’s Happy Meals or Subway sandwiches provided by interrogators when they think other detainees won’t find out.

And while detainees have complained of wounds from the repeated insertion and removal of the tubes, the military says it uses lubricants and local anesthetics to ease the pain.

Health experts unaffiliated with the military say there are no nutritional consequences from long-term tube feeding, that with proper care it can be done safely.