The top US diplomat was expected to meet President Hamid Karzai for talks before lunch, as she seeks to build on the "diplomatic surge" she announced earlier this year, a senior state department official told travelling media.

Ten years after the US-led invasion, Karzai's reconciliation efforts were derailed by the September assassination of peace broker Burhanuddin Rabbani and the militia are perceived to pose an increasingly wide threat in Afghanistan.

Concern is also growing among Afghans about the prospect of increased violence after 2014, when the US-led NATO mission is scheduled to withdraw all combat troops and hand over responsibility to local Afghan security forces.

"She wants to signal US support for a secure and stable Afghanistan," a senior State Department official told reporters on condition of anonymity.

"She will want to emphasise that the United States remains committed to Afghan reconciliation," he added, particularly in the wake of the September 20 assassination of Rabbani, a former president of Afghanistan.

Before meeting Karzai, Clinton was to talk to civil society leaders in the capital, including Rabbani's son Salahuddin Rabbani, who now heads his father's political party, the Islamic Party of Afghanistan.

Another official said a conference of regional powers to be held in Istanbul in early November, and an international meeting of foreign ministers in Bonn, Germany, in early December, would be part of discussions.

After 10 years of military conflict in Afghanistan that has cost thousands of lives and hundreds of billions of dollars, Washington is grappling for a negotiated exit to the war ahead of the 2012 US presidential elections.