Get the latest military news and headlines delivered to your inbox every weekday morning.
US Defense Secretary Leon Panetta on Friday voiced frustration at Afghan President Hamid Karzai over the latter's preference to "criticize" American troops, instead of acknowledging the sacrifices they made.
Panetta, who arrived in Peru to begin a Latin American tour, earlier told reporters aboard the military plane taking him to Lima that Karzai should remember that more than 2,000 US troops had died in Afghanistan.
The angry riposte came after Karzai said on Thursday that the United States was failing to go after militants based in Pakistan, another charge that Panetta chose to hit back at.
"We have made progress in Afghanistan because there are men and women in uniform who are willing to fight and die for Afghanistan's sovereignty and their right to govern and secure themselves," Panetta said.
"We've lost over 2,000 US men and women, ISAF has lost forces there and the Afghans have lost a large number of their forces in battle.
"Those lives were lost fighting the right enemy, not the wrong enemy. And I think it would be helpful if the president, every once in a while, expressed his thanks for the sacrifices that have been made by those who have fought and died for Afghanistan rather than criticize."
The outburst was rare for Panetta and the remarks come as relations between the United States and Afghanistan come under strain in the wake of several deadly and high-profile attacks on American troops by their local comrades.
In Afghanistan, the United States has also seen its image tarnished among ordinary Afghans this year by the burning of Korans at a military base, the abuse of corpses and a massacre of civilians by a rogue American soldier.
An unprecedented number of Afghan security personnel have turned their weapons against their allies, killing at least 51 NATO soldiers this year.
Despite this, many Afghans, particularly in the cities, fear the departure of the Western troops in 2014 from a country where the government of Karzai is widely seen as corrupt and dependent on foreign support.