'Significant progress' on talks with Taliban, says US envoy

However, Zalmay Khalilzad, the US Special Representative for Afghanistan Reconciliation, cautioned that nothing has been finalised yet.

Afghanistan-born Khalilzad said this in a series of tweets after six days of talks with the Taliban representatives in Doha, Qatar. He now heads to Kabul for consultations with the elected Afghan government.

"After six days in Doha, I'm headed to Afghanistan for consultations. Meetings here were more productive than they have been in the past. We made significant progress on vital issues," he said Saturday.

"Will build on the momentum and resume talks shortly. We have a number of issues left to work out. Nothing is agreed until everything is agreed, and 'everything' must include an intra-Afghan dialogue and comprehensive ceasefire," Khalilzad said.

The top American diplomat thanked Qatar for their constructive engagement and their facilitation of this round of talks.

Since being appointed in September last, Khalilzad has met with all sides in an attempt to end America's longest war.

The Taliban control nearly half of Afghanistan, and are more powerful than at any time since the 2001 US-led invasion.