US defence secretary Jim Mattis believes victory in Afghanistan is still possible, though not necessarily on the battlefield but in facilitating a Taliban reconciliation with the country's government.
Mr Mattis was speaking shortly before arriving in Kabul, amid high security concerns, where he will meet President Ashraf Ghani and top US commanders.
He said "we do look towards a victory in Afghanistan". However, he added that it would not be a military victory but "the victory will be a political reconciliation" with the Taliban, which has achieved a stalemate in recent years and shown little interest in conceding to the Kabul government.
Mr Mattis, a retired marine general who commanded US troops in southern Afghanistan in the opening weeks of the war in 2001, said getting the Taliban to reconcile en masse may be "a bridge too far". So the emphasis is on drawing in Taliban elements piecemeal.
He described this approach as an effort to "start peeling off those who are tired of fighting" after more than 16 years of war.
"We know there is interest on the Taliban side," he said.
He defined victory in Afghanistan as a political settlement between the Taliban and the government, and an Afghan military that is capable of securing the country largely on its own.
At that point, he said, Afghanistan would not be "a haven for attacks internationally" as it was when al Qaida used the country as a launching pad for the attacks of September 11 2001.
US intelligence officials are predicting the war will remain stalemated as the traditionally most intensive fighting season begins this spring.
The visit is Mr Mattis's second since President Donald Trump announced last August that, despite his instinct to pull US troops out of Afghanistan, his administration would take a more aggressive approach to the conflict, now in its 17th year.
As part of an effort to bolster Afghan fighting strength, the US in recent weeks sent an army group of about 800 soldiers, accompanied by several hundred support troops, to advise the Afghans closer to the front lines.
The US also shifted A-10 attack planes and other aircraft from striking Islamic State militants in Syria and Iraq to Afghanistan as part of Mr Trump's new approach. These and other moves boosted the number of US troops in Afghanistan by at least 3,500 to a total of more than 14,000.
Mr Mattis has said that the US goal is to enable Afghan forces to weaken the Taliban to the point where the Afghans can manage their own security. Put another way, the aim is to convince the insurgents they cannot win on the battlefield, thus driving them to reconcile with the Afghan government.