US President Donald Trump has said Secretary of State Mike Pompeo will witness the signing of a US-Taliban agreement on a withdrawal of American troops from Afghanistan.

The deal, part of a wider push for Afghan reconciliation and an end to the longest US war, faces many obstacles, including an election feud between Afghanistan’s two leading politicians.

It is expected to be signed in Qatar’s capital Doha on Saturday.

The US-Taliban agreement would begin a phased withdrawal of American and coalition forces.

It would require the Taliban to initiate a formal dialogue with the Afghan government and other political and civil society groups on a permanent nationwide ceasefire and power sharing in postwar Afghanistan.

US forces invaded the Southwest Asian country in 2001 to topple the Taliban rulers who provided a safe haven in which al Qaeda planned the September 11, 2001, attacks on New York and the Pentagon that killed nearly 3,000 people.

Among the many obstacles to peace are resolving a dispute between Afghan President Ashraf Ghani and his main political rival, Chief Executive Abdullah Abdullah.

Both have claimed victory in the disputed September 28 presidential election.

There is also the undecided question of who will form the Afghan team that would negotiate with the Taliban on how to bring the insurgents into the political process and, ultimately, how to share power with the movement.

The agreement calls for a long-planned initial drawdown to 8,600 US troops from some 13,000 but it ties further cuts to the Taliban keeping promises it may find challenging, such as cutting deep ties with al Qaeda and other militant groups.

Earlier, Pompeo told US lawmakers he had seen a “significant” reduction of violence in Afghanistan over the past six days.

Afghan officials met Taliban members in Qatar on Friday to discuss a prisoner swap plan.

Trump has made withdrawal of U.S. troops from Afghanistan a major foreign policy objective. An agreement with the Taliban to end the 18-year-old war could boost his re-election prospects.