The report, written on the day of the hikers' arrest July 31, says the Americans ignored unspecified cautions about their travels. The report also predicted Iran would accuse the three of spying, which it later did.
"The leadership in Iran benefits as it focuses the Iranian population on a perceived external threat rather than internal dissension," the report said.
The document, a field report not meant as a definitive account or a conclusive assessment, was first reported by The New York Times on its website Friday. It was among nearly 400,000 secret U.S. military documents revealed by WikiLeaks.
Although the documents appear to be authentic, their origin could not be independently confirmed, and WikiLeaks declined to offer any details about them. The Pentagon has previously declined to confirm the authenticity of WikiLeaks-released records, but it has employed more than 100 U.S. analysts to review what was previously released and has never indicated that any past WikiLeaks releases were inaccurate.
In Friday's release, names and other pieces of identifying information appeared to have been redacted but it was unclear to what extent WikiLeaks withheld names in response to Pentagon concerns that people could become targets of retribution.
The U.S. military report described "a kidnapping of 3 Americans who were being taken to the Iranian border. The Americans were hiking near the Iranian border when taken."
An update later in the day said an Iraqi colonel reported that the three had been detained "for being too close to the border." The State Department has repeatedly urged Iran to release the three - Sarah Shourd, Shane Bauer and Josh Fattal, saying they did nothing wrong. Iran claims they illegally crossed the border to spy.
Shourd was released in September after complaining of health problems; the two others remain in prison in Iran.