The last of the 33,000 US soldiers that President Barack Obama sent to Afghanistan nearly three years ago as part of a military surge have left the country, US defense officials said.
The withdrawal, which began in July, follows an unprecedented number of NATO soldiers being shot dead by their Afghan colleagues -- 51 so far this year -- and comes as anti-Western protests sweep Muslim countries.
There are still some 68,000 US military forces in Afghanistan, as well as some 40,000 from NATO's ISAF coalition.
The US-led effort to contain the Taliban insurgency involves a phased withdrawal of troops as newly trained Afghan forces take their place. The plan is for Afghans to take charge of their own security by the end of 2014.
The temporary increase in troops helped Western-led forces regain ground in Afghanistan's south and southwest against the Taliban, which has now stepped up attacks in the eastern region bordering Pakistan.
Defense Secretary Leon Panetta said on Thursday the surge had met its goals of reversing the Taliban's momentum and "dramatically" increasing the size and capability of Afghan security forces.
"At the same time, we have struck enormous blows against Al-Qaeda's leadership, consistent with our core goal of disrupting, dismantling and defeating Al-Qaeda and denying it a safe-haven," he said in a statement.
However, he stressed that with tens of thousands of US troops still engaged in a tough fight in Afghanistan, "We are a nation at war."
"But the international community is also strongly united behind our shared strategy to transition to Afghan security control," he added.
Decisions are pending on the pace of future withdrawals.
On Tuesday, NATO announced that it would limit joint operations with Afghan forces, marking a setback to the US-led strategy for containing the decade-old Taliban insurgency.
Australian Brigadier-General Roger Noble, deputy to ISAF's operations chief, said the string of insider attacks had been dispiriting.
Noble said the decision to scale back joint operations was "just normal military business and common sense," and insisted it would not derail the drawdown effort.
"The campaign remains on track to achieve its objectives," Noble told Pentagon reporters, speaking from Kabul.