KABUL (Reuters) - The Taliban on Friday issued a new video tape of a captured American soldier ridiculing the war in Afghanistan as "our next Vietnam," a move the U.S. military condemned as a cruel piece of Christmas Day propaganda.

The parents of Idaho National Guard Private Bowe Bergdahl, who was taken prisoner in Afghanistan this summer and is the only known U.S. soldier in captivity there, issued an appeal for his release and urged their son to "stay strong."

Bergdahl, whose identity was confirmed by his family, appears in the video wearing sunglasses and a U.S. military-style uniform, including a military helmet.

He gives his name, hometown and other personal details before saying he is a prisoner of war of the Taliban. It is not clear when the video, the second of him released since his capture, was made.

He goes on to attack U.S. leaders for their treatment of Muslims in Iraq and Afghanistan and warns that the military is no match for the Taliban.

"I'm afraid to tell you that this war has slipped from our fingers and it's just going to be our next Vietnam unless the American people stand up and stop all this nonsense," he says.

But a military spokesman said the statements should be considered coerced, and condemned the timing of its release.

"This is a horrible act which exploits a young soldier, who was clearly compelled to read a prepared statement. It reflects nothing more than the violent, deceitful tactics of the Taliban insurgency," said U.S. Navy Rear Admiral Gregory Smith, director of communication, with NATO-led forces in Afghanistan.

"To release this video on Christmas Day is an affront to the deeply-concerned family and friends of Bowe Bergdahl, demonstrating contempt for religious traditions and the teachings of Islam. We will continue our search for Bowe Bergdahl," he said in a written statement.

'STAY STRONG'

Bergdahl's parents, who live near the central Idaho town of Hailey, just south of the upscale Sun Valley ski resort, were notified of the video on Friday, said Lieutenant Colonel Timothy Marsano of the Idaho National Guard.

"The Bergdahl family pleads with the captors to let our only son come home," his parents said in a brief statement issued on their behalf by Marsano. They added: "To Bowe: we love you and we believe in you. Stay strong."

The parents, who Marsano declined to further identify, were unable to view the video for themselves because of a major power outage that left them without television or Internet service on Friday. They spoke instead with a relative elsewhere in the state who had seen it, and it was described to them.