Mattis's remarks came as he flew into the war-torn city, weeks after Afghan President Ashraf Ghani unveiled a plan to open peace talks with the Taliban. The insurgents have so far given no formal response to Kabul's offer for negotiations.

But Mattis said some insurgent leaders have expressed an interest in discussions.

"It may not be that the whole Taliban comes over in one fell swoop, that would be a bridge too far, but there are elements of the Taliban clearly interested in talking to the Afghan government," Mattis told reporters aboard a military jet.

Ghani's peace plan includes eventually recognising the Taliban as a political party.

The insurgent group has said it was prepared to negotiate, but only with the US and not with the Kabul government.

"Right now we want the Afghans to lead and to provide the substance of the reconciliation effort," Mattis said.

Thanks to the political process, Mattis said America is now looking towards victory in Afghanistan after more than 16 years of conflict.

"What does that victory look like? It's a country whose own people and their own security forces handle law enforcement and any threats... certainly with international support for some years to come," he said.

Mattis's talk of a victory comes amid renewed US focus on Afghanistan after years of drawdowns under former president Barack Obama and talk by top US generals of "not winning" and of a "stalemate" in the seemingly intractable conflict.

"It's all working to achieve a political reconciliation, not a military victory," Mattis said.

"The victory will be a political reconciliation."

As part of the so-called South Asia Strategy, President Donald Trump last year ordered the increased bombing of Taliban targets -- including their drug-making labs and training camps -- and more than 3,000 additional US forces have arrived in Afghanistan to boost the training and advising of local troops.

Approximately 14,000 American forces are now in Afghanistan, up from a low of about 8,500 when Obama left office.

Ghani's offer of peace talks comes as civilian casualties have soared in recent months, with the Taliban increasingly targeting towns and cities in response to Trump's new and more aggressive US military policy.

The Taliban, Afghanistan's biggest militant group, claimed 472 attacks in January alone, the Washington-based terrorism research group TRAC said -- an astonishing number given that the traditional fighting season doesn't usually start until freezing temperatures have subsided in the spring.