Ambassador James Cunningham said reconciliation is "a process that hasn't even really begun," the British publication The Guardian reported Thursday.
Cunningham said one of Washington's goals was ensuring there was "at least the beginning of a serious process."
Cunningham also expressed concerns about the unconditional release of some Taliban prisoners held in Pakistan, which was done at the request of Afghan leaders and seen as a goodwill effort meant to help the negotiation process.
"To this point they've had a pretty hands-off kind of approach to the people that they have released," Cunningham said. "We would have preferred to have greater visibility into that. Still, it's positive that they were released, I think, from the Afghan point of view."
U.S., Afghan, Pakistani and Taliban officials have been meeting for months, focused on initiatives such as the Taliban opening a political office outside the immediate region and the release of Taliban prisoners to help get peace talks rolling after years of fits and starts.
Earlier this month Taliban leaders said they were ready to open an office in Qatar to conduct negotiations "with the international community," The Guardian said.
Since last November, Pakistan has released Taliban prisoners three times.
Cunningham said the United States hoped to begin substantive talks soon.
"What we would like to see, and what I think the Afghans would like to see, is ... if not the conclusion of a negotiation, at least the beginning of a serious process on peace and reconciliation as soon as possible," Cunningham said.