Washington (CNN) -- The U.S. military has obtained a new video made by those holding Sgt. Bowe Bergdahl, the U.S. soldier who was taken captive in Afghanistan in June 2009 and is believed held by the Taliban-aligned Haqqani network in Pakistan, a U.S. military official tells CNN.

The video, which has been described to CNN by the official, shows Bergdahl in diminished health from the effects of close to five years in captivity.

The proof-of-life video has a reference to December 14, 2013. CNN has contacted Bergdahl's family. The military says that it keeps the family aware of developments regarding his case.

Bergdahl is the only American soldier in captivity, and this the first video of him in three years. The previous one was sent in February 2011. Last year, Bergdahl's family received a letter from him via the Red Cross. CNN has not seen the video, but its contents have been described to the network.

U.S. efforts to free Bergdahl, including negotiating for his release, have so far failed.

"Sgt. Bowe Bergdahl has been gone far too long, and we continue to call for and work toward his safe and immediate release," a Pentagon spokesman told CNN, "We cannot discuss all the details of our efforts, but there should be no doubt that on a daily basis -- using our military, intelligence and diplomatic tools -- we work to see Sgt. Bergdahl returned home safely."