The top US negotiator on Afghanistan said Tuesday he was ready to conclude peace talks with the Taliban as he headed back to Qatar on a mission to end the US' longest war.

With US President Donald Trump believed to be pushing for a pullout of the more than 13,000 US troops in Afghanistan before the November 2020 election, the talks are expected to focus on establishing a timeline for the US withdrawal in exchange for a "reduction in violence" and a Taliban pledge to not protect the Islamic State or Al Qaeda.

"We've been there for 18 years - it's ridiculous," Trump told reporters shortly after the announcement that his envoy Zalmay Khalilzad was returning to the Qatari capital Doha for another round of talks.

"We are negotiating with the government and we are ­negotiating with the Taliban," he said.

"We have good talks going and we will see what happens."

Khalilzad, the US special representative for Afghanistan reconciliation, bolstered optimism for a peace agreement last week when he concluded the eighth round of negotiations with the Islamist insurgents with a tweet saying he hoped this is the final year that the country is at war.

The veteran diplomat also has to prepare the ground for peace talks between the Taliban and the Afghan government, which would come after any deal with Washington.

"Productive week in Washington. Briefed management on where we are and next steps," Khalilzad tweeted as he headed to Qatar.

"Back on the road again. First stop Doha where we will try and close on remaining issues. We're ready. Let's see if the Taliban are as well."

The State Department said he will head to Afghanistan ­after Doha where he plans to help prepare the ground for Kabul-Taliban talks.

Earlier Tuesday US Secretary of State Mike Pompeo told CNBC television that a deal in Doha was possible, if the current level of attacks in the country can be significantly reduced.

"The conversations are going well," Pompeo said.