(CNN) -- Photos of U.S. soldiers posing with bodies of suspected Afghan urgents, published Wednesday by the Los Angeles Times, depict behavior that "absolutely violates" U.S. regulations and values, Defense Secretary Leon Panetta said Wednesday.
"This is not who we are, and it's certainly not who we represent when it comes to the great majority of men and women in uniform who are serving there," he said.
The two photos published by the paper are among 18 provided by a U.S. soldier who wanted "to draw attention to the safety risk of a breakdown in leadership and discipline," The Times reported.
The military said an investigation is under way.
NATO Secretary-General Anders Fogh Rasmussen said the images "don't in anyway represent the principles and values that are the basis for our mission in Afghanistan." He added that he considers the photos "an isolated event."
The photos, from incidents in 2010, represent "a serious error in judgment by several soldiers who have acted out of ignorance and unfamiliarity with U.S. Army values," NATO'S International Security Assistance Force said in a statement. Gen. John Allen, the ISAF commander, also condemned the photos.
One shows a member of the U.S. military in front of what appears to be the body of an insurgent. The photo shows the insurgent's head, with his eyes open and what may be his hand on the American soldier's shoulder. Another soldier appears to be looking down at the body, reaching his hand into the blanket covering it.
"A soldier from the Army's 82nd Airborne Division with the body of an Afghan insurgent killed while trying to plant a roadside bomb," the caption reads. "The photo is one of 18 provided to The Times of U.S. soldiers posing with corpses."
The second photo shows a group of people, including some American soldiers, standing with what appear to be legs from a dead body. One U.S. soldier is smiling and giving a double thumbs-up, and another is also smiling at the camera. There appear to be Afghan police in that photo as well.
The paper says the photo was from 2010, when the division arrived at a police station in Zabul province and inspected body parts. "Then the mission turned macabre: The paratroopers posed for photos next to Afghan police, grinning while some held -- and others squatted beside -- the corpse's severed legs."