US Secretary of State Hillary Clinton said only a political solution will end the war in Afghanistan and voiced hope that rank-and-file Taliban could be split off from Al Qaeda extremists.

In a speech at the Asia Society in New York on Friday, Clinton reaffirmed US plans to start reducing troops in July and complete the drawdown by the end of 2014 as Afghans take charge of their war-torn country.

Clinton said the surge in US-led troops over the past year was part of a strategy to "split the weakened Taliban off from Al Qaeda and reconcile those who will renounce violence and accept the Afghan constitution."

"I know there are some on Capitol Hill and elsewhere who question whether we need anything more than guns, bombs and troops to achieve our goals in Afghanistan," Clinton said.

"As our commanders on the ground will be the first to say, that is a short-sighted and ultimately self-defeating view. We will never kill enough insurgents to end this war outright," Clinton said.

The relationship between Al Qaeda and the Taliban has long been a source of contention within US policy circles.

After the September 11 attacks, President George W. Bush's administration described the two groups as virtually indistinguishable. US troops, now led by General David Petraeus, have focused on taking the fight to the Taliban.

But key civilian leaders under President Barack Obama have put a focus on political reconciliation, arguing that many rank-and-file Taliban are simply seeking a livelihood and can be co-opted.

Meanwhile, The New Yorker magazine reported on Friday that the Obama administration has entered into direct, secret talks with senior Afghan Taliban officials.

The talks were characterized in the story as an attempt by the Obama administration "to assess which figures in the Taliban's leadership, if any, might be willing to engage in formal Afghan peace negotiations, and under what conditions."

Pulitzer Prize-winning journalist Steve Coll wrote that several sources, which were not identified in the story, briefed him about the talks.

Clinton said that the Taliban faced a similar choice as in 2001, when the United States toppled the hardline Islamic regime for hosting Al Qaeda leaders who planned the September 11 attacks on New York and Washington.

"Today, the escalating pressure of our military campaign is sharpening a similar decision for the Taliban: break ties with Al Qaeda, renounce violence and abide by the Afghan constitution and you can rejoin Afghan society.

"Refuse and you will continue to face the consequences of being tied to Al Qaeda as an enemy of the international community," Clinton said.

"They cannot wait us out. They cannot defeat us. And they cannot escape this choice."

Clinton acknowledged that reconciliation with the Taliban may sound "distasteful, even unimaginable." She pledged to keep up pressure to safeguard the rights of women, which were severely curtailed by the Taliban regime.

"Diplomacy would be easy if we only had to talk to our friends. But that is not how one makes peace," Clinton said.

Clinton was delivering an inaugural lecture in memory of hard-charging US diplomat Richard Holbrooke, who served as Washington's special envoy to Afghanistan and Pakistan and was a leading advocate for a political settlement.

Holbrooke, a former chair of the Asia Society, died suddenly on December 13 of a torn aorta. He was 69.

Clinton announced the appointment of Holbrooke's successor: Marc Grossman, a retired career diplomat who has served in Pakistan and Turkey and rose to the top position of undersecretary of state for political affairs.

Grossman will face major challenges including a crisis with Pakistan over its detention of a US government employee accused of shooting two Pakistanis — an issue Clinton did not mention in her wide-ranging speech.

Clinton said it was "no secret that we have not always seen eye-to-eye with Pakistan." Al Qaeda and Taliban fighters are largely holed up in the lawless Northwest of Pakistan, whose government is allied with the United States.

"Pressure from the Pakistani side will help push the Taliban towards the negotiating table and away from Al Qaeda," she said.