Afghanistan and the United States Friday marked 10 years since the US went to war against the Taliban, triggering a decade-long conflict that has cost thousands of lives and billions of dollars.

US President Barack Obama honored all those killed since the start of the conflict launched against the Taliban regime in the wake of the September 11, 2001 Al-Qaeda attacks on the United States.

"Ten years ago today, in response to the 9/11 terrorist attacks, our nation went to war against Al-Qaeda and its Taliban protectors in Afghanistan," Obama said, calling it a "decade of sacrifice."

He saluted "the more than half a million men and women who have served bravely in Afghanistan to keep our country safe, including our resilient wounded warriors who carry the scars of war, seen and unseen."

"We honor the memory of the nearly 1,800 American patriots, and many coalition and Afghan partners, who have made the ultimate sacrifice in Afghanistan for our shared security and freedom," the US president added.

On October 7, 2001, American planes dropped dozens of cruise missiles and laser-guided bombs on strategic targets in Kabul and other Afghan cities after the Taliban refused to surrender Osama bin Laden following the 9/11 attacks.

Within weeks, the Islamic Taliban regime had crumbled under the onslaught of Operation Enduring Freedom. Its fighters had fled and Afghans poured out of their homes celebrating the collapse of one of the most repressive regimes in modern times.

The Pentagon puts the cost of the operation at $323.2 billion, while Brown University researchers say at least 33,877 people -- foreign and Afghan troops, civilians, insurgents and others -- have died. Of those 1,788 US troops have been killed, and 14,342 wounded, according to the Pentagon.

Ten years on, some US officials see a political settlement with the people they bombed out of power as the answer to resolving one of its longest wars in history that today outstrips the 10-year Soviet misadventure in Afghanistan.

Stanley McChrystal, commander in Afghanistan until he was sacked in 2010, delivered a speech on the eve of the anniversary saying the US-led NATO mission was "a little better than" halfway to achieving its military goals.

"We didn't know enough and we still don't know enough," he said, adding the United States and its allies had a "frighteningly simplistic view" of recent history.

"When we arrived we were woefully underinformed, we also didn't have the tools to get informed: we didn't speak the language," the retired four-star general said.

And he added that the subsequent invasion of Iraq made things "more difficult because it changed the Muslim world view of America's effort."

As the United States turned its focus to Iraq, committing tens of thousands of troops and billions of dollars to ousting Saddam Hussein, the Taliban began to transform from a rag-tag bunch of renegades into a well-disciplined militia.

Outside the White House on Friday, more than 200 protesters filed past, denouncing the war in Afghanistan, carrying model drones and banners that demanded an immediate NATO pullout.

But in Afghanistan, the anniversary passed without public commemoration by either the Afghan government or NATO while on the frontline, and it was business as usual for the 140,000 foreign troops still stationed there.

The anniversary also highlighted antagonism at Western troops, anger over thousands of civilian casualties and corruption within the government of President Hamid Karzai, propped up by the United States and its foreign allies.

"We will be very pleased if they pull out from Afghanistan," said street vendor Khan Agha, 30. "The US and its allies didn't do good when they invaded.

"Despite all the hard times, we had good security in the Islamic regime of the Taliban."

Obama said the United States was "responsibly ending today's wars from a position of strength" though he warned "enormous challenges" remained.

But Karzai himself said his government and the US-led NATO mission had done "terribly badly in providing security to the Afghan people and this is the greatest shortcoming of our government and of our international partners."

Writing in British newspaper The Daily Telegraph under the headline "It's a fantasy to think we are winning the war in Afghanistan," former British ambassador to Kabul, Sherard Cowper-Coles, was scathing of Western strategy.

Military operations, he wrote, "are not curing the underlying disease" of the insurgency and only "a Herculean effort of American-led diplomacy" can correct the errors and omissions of the last decade.

Efforts to broker peace with the Taliban had made scant progress even before the September 20 assassination of Karzai's peace envoy Burhanuddin Rabbani threw the government strategy for brokering a settlement into turmoil.

Some experts fear the country could be sliding back towards the kind of civil war that killed and displaced thousands of people in 1992-96.