Taliban spokesman Zabihullah Mujahid said Panetta's two-day trip was aimed at boosting the morale of American troops, but it was the insurgent fighters who were in fact gaining strength.
"These remarks by the highest ranking US military official are just meant to boost the morale of their soldiers and hide their defeat," he said in a statement highlighting the ongoing propaganda war.
Despite 10 years of war, western analysts admit they have "not achieved even one percent success despite their pressure", he added.
"New mujahedeen have been entering the ranks of Taliban every day. They conduct attacks with new tactics and higher morale on occupying troops in every corner of the country, even in the ongoing cold weather.
"All these facts are proofs of our war achievements."
Panetta was in Afghanistan to review the war effort with the United States, which is on track to recall 33,000 troops by the end of the next year and is shifting its focus to an advisory role in training Afghan security forces.
"We're moving in the right direction and we're winning this very tough conflict," he told US troops Wednesday.
There are around 140,000 international troops in Afghanistan helping pro-government forces fight a drawn-out 10-year Taliban-led insurgency that has cost thousands of lives, billions of dollars and wearied Western voters.
All foreign combat troops are due to leave by the end of 2014, but a sizeable troop mission to train and mentor national forces is set to remain beyond that date.
Despite the tight timetable for the transition of security, the military and the United Nations disagree over the extent to which violence is really falling in Afghanistan.
In October, the Pentagon said that Taliban attacks were down for the first time in five years but the UN says the number of civilians who were killed increased by 15 percent in the first six months of this year.
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