President Donald Trump will complete a campaign promise and end America's longest war, the Afghanistan War, in a brokered peace deal with the Taliban.

US officials are set to sign the deal on Saturday.

"Nearly 19 years ago, American service members went to Afghanistan to root out the terrorists responsible for the 9/11 attacks. In that time, we have made great progress in Afghanistan, but at great cost to our brave service members, to the American taxpayers, and to the people of Afghanistan," said Trump in a statement on Friday.

"When I ran for office," he added, "I promised the American people I would begin to bring our troops home, and seek to end this war. We are making substantial progress on that promise."

The Afghanistan War began in 2001 when President George W. Bush ordered the assault on terrorist elements. The bombings were in response to the 9/11 attacks by al Qaeda that killed almost 3,000 Americans.

The war has cost the US more than $750 billion.

The president told reporters that Secretary of State Mike Pompeo will personally witness the signing of the peace deal. It is unclear if the president will have any personal involvement with the signing with representatives of the Taliban.

In September, the president revealed in a tweet that he had called off a secret meeting with members of the Taliban at Camp David after an attack that took the lives of several US military members.

"Unfortunately, in order to build false leverage, they admitted to an attack in Kabul that killed one of our great great soldiers, and 11 other people," he tweeted. "I immediately cancelled the meeting and called off peace negotiations. What kind of people would kill so many in order to seemingly strengthen their bargaining position?"

The Taliban responded to the cancelled meeting by claiming it would lead to more US deaths. Only five months later, the president announced the peace deal.

Trump made it a campaign promise to end the United States' involvement in "endless wars" during the 2016 presidential campaign.

That promise to the American voters will be completed on Saturday.

Here's the latest on the peace deal: