Such behavior on the part of U.S. troops in Afghanistan "show a lack of judgment, a lack of professionalism and a lack of leadership" and damages U.S. national interests, Panetta said.
"These days, it takes only seconds for one picture to suddenly become an international headline. And those headlines can impact the mission we're engaged in, they can put your fellow service members at risk, they can hurt morale, and they can damage our standing in the world."
While such episodes "represent a very, very small percentage of the great work that our men and women do every day across the world," Panetta said, "They concern us because our enemies will seek to turn them in their favor, at the very moment when they are losing the wider war. …
"Never forget that you have a responsibility to look after your fellow soldiers and to represent the American people that you are sworn to defend," Panetta said.
"We have an enduring commitment to Afghanistan and to the Afghan people. And if we keep our eye focused on this mission, as I know you all will, we will defeat al-Qaida; we will deny them the ability to rebuild; we will deny them the safe haven that they used to plan an attack on our country.
"They may have attacked us once; they will not do it again. Too much precious blood has been spilled, too much progress has been made to lose sight of the mission now."
2014: The Year in Music [PHOTOS]