"I'd say really the takeaway right now: it's encouraging," Shanahan told Pentagon reporters as he waited to greet NATO Secretary General Jens Stoltenberg.

Shanahan's remarks came after US special envoy Zalmay Khalilzad was quoted Monday as saying the US and the Taliban have drafted the framework of a deal which could pave the way for peace talks with Kabul.

Khalilzad has been leading a months-long diplomatic push to convince the Taliban to negotiate with the Afghan government, but the militants have steadfastly refused, dismissing authorities in Kabul as "puppets."

US officials have said President Donald Trump wants to withdraw about half of the 14,000 US troops in Afghanistan.

Shanahan did not provide details about potential US troop withdrawals.

In response to a reporter's question, he said he had not been tasked to prepare for a "full" withdrawal.

Stoltenberg later said it was too early to speak about the future disposition of NATO forces in Afghanistan.