A US Army officer has accused the American military of painting a misleading picture of progress in the war in Afghanistan while glossing over the Kabul government's many failings.

Lieutenant Colonel Daniel Davis deliberately broke ranks with the official portrayal of the war after spending a year in the country, issuing a grim assessment and accusing his superiors of covering up the harsh realities that plague the mission.

"What I saw bore no resemblance to rosy official statements by US military leaders about conditions on the ground," Davis wrote in an article published in Armed Forces Journal, a private newspaper not affiliated with the Pentagon.

"Instead, I witnessed the absence of success on virtually every level," he wrote under the headline, "Truth, Lies And Afghanistan: How military leaders have let us down."

Local Afghan government officials are failing to serve the Afghan population and their security forces are reluctant to fight insurgents or are colluding with the Taliban, he wrote.

"How many more men must die in support of a mission that is not succeeding and behind an array of more than seven years of optimistic statements by US senior leaders in Afghanistan?" he said in his article.

Davis has also reportedly shared his pessimistic view with some members of Congress and written a classified version of his article for the Defense Department, a highly unusual move that he expects will anger his commanders and short-circuit his professional career.

"I'm going to get nuked," he was quoted as saying by the New York Times.

The Pentagon politely disagreed with Davis's portrayal of the war but stopped short of suggesting any disciplinary action.

"Lieutenant Colonel Davis is obviously entitled to his opinion," spokesman George Little told reporters, adding that Defense Secretary Leon Panetta "has very strong confidence in his commanders in Afghanistan, as they provide assessments of what's happening on the ground in the war."

The military's evaluation of the war effort is based on "rigorous analysis" from a myriad of sources and does not depend on one person's view, he said.

Working with the US military's Rapid Equipping Force, Davis said he traveled 9,000 miles (14,500 kilometers) around Afghanistan and spoke with more than 250 soldiers during his 12-month deployment.

His comments and anecdotes reflect opinions often expressed by American and coalition troops, who make no secret of their frustrations with Afghan security forces.

Davis recounted a conversation with an Afghan police officer in eastern Afghanistan in Kunar province less than three hours after an insurgent attack.

Through an interpreter, Davis asked the police captain how his forces usually responded to such an incident and if his squad would go after the insurgent fighters.

The Afghan police officer gave him an incredulous look, laughed and said: "'No! We don't go after them,' he said. 'That would be dangerous!'"