The United States is preparing to sign a deal with the Taliban on February 29, building on an agreement on reducing violence across Afghanistan, Secretary of State Mike Pompeo said Friday.

"Upon successful implementation of this understanding, signing of the US-Taliban agreement is expected to move forward," he said in a statement released after visiting Saudi Arabia.

A week-long "reduction in violence" between the Taliban, the US and Afghan security forces will commence shortly, Afghanistan's National Security Council spokesman Javed Faisal said on Friday.

The partial truce will mark a historic step in more than 18 years of gruelling conflict in Afghanistan and would pave the way for a deal that could, ultimately, see the war ended.

Pompeo said that intra-Afghan negotiations would begin shortly after the February 29 signing, expected to take place in the Qatari capital Doha.

They will "build on this fundamental step to deliver a comprehensive and permanent ceasefire and the future political roadmap for Afghanistan," he said.

The US top diplomat said that challenges remain, but that progress made so far "provides hope and represents a real opportunity. The United States calls on all Afghans to seize this moment".