Lt. Gen. John Lorimer told the BBC in interview that Afghan forces are showing "resilience" against Taliban attacks and despite rising casualties, the forces are taking on the insurgents.
The general's assessment comes as NATO troops, winding down their operations in Afghanistan, hand over security responsibility to local forces. The U.S.-led NATO forces will end their combat operations by the end of next year.
Taliban violence has escalated sharply in the current environment, and the BBC said the insurgent attacks have resulted in scores of civilians deaths in recent days.
"When you are fighting a ruthless enemy, inevitably you are going to take some casualties," said Lorimer.
Lorimer, who is the NATO's second-in-command in Afghanistan, said the Afghan military is "well trained."
"They're developing leaders," the general said. "They are going on the front foot, taking the fight to the insurgents."
The BBC report said the general's remarks will be seen as a vote of confidence in the Afghan security forces, which are now leading combat operations ahead of NATO's withdrawal.
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