Mattis confirms decision made on path forward in Afghanistan

US President Donald Trump waves upon his arrival at Air Force One at Hagerstown Regional Airport in Hagerstown, Maryland at the weekend. Photo / AP

US Defence Secretary Jim Mattis confirmed that a decision has been made on a military strategy in Afghanistan, where more than 8000 troops already are based in the longest-running war in US history.

Speaking to reporters on a military plane en route to meetings in Jordan, Mattis said it is up to US President Donald Trump to announce the details of a review of US policy in Afghanistan and South Asia.

The White House announced that Trump would address the nation's troops and the American people - his first prime time address - tomorrow.

The results have been delayed amid concerns that, more than 15 years after the US invaded, an international coalition working together with Afghan forces are not winning the fight against the Taliban and al-Qaeda.

"I am very comfortable that the strategic process was sufficiently rigorous and did not go in with a preset position," Mattis told reporters. "The President has made a decision. As he said, he wants to be the one to announce it to the American people."

On Saturday, Trump met at Camp David to discuss Afghanistan strategy with more than a dozen aides, including Mattis, Secretary of State Rex Tillerson, National Security Adviser H.R. McMaster and Vice-President Mike Pence.

After the briefing, White House press secretary Sarah Huckabee Sanders said Trump was "studying and considering his options". Then Trump tweeted that at Camp David, "many decisions [were] made, including on Afghanistan".

A variety of options have been under consideration, including sending about 3800 more troops to augment the 8400 already there to train and assist local forces. Another option Mattis has mentioned is to replace US troops with private contractors.

But any proposal to reinforce the US presence there is certain to meet resistance.

Senator Benjamin Cardin of Maryland, the ranking Democrat on the Senate Foreign Relations Committee, said on Fox News Sunday that he will oppose sending more troops.

"I don't believe putting more American soldiers in Afghanistan is the answer," he said, arguing that a stable government in the country should be the goal.

Trump has given Mattis authority to set troop levels in the country, but Mattis has been waiting for Trump to decide a strategic focus before he sends any more troops.

Trump has expressed frustration over the lack of a clear way forward as the war drags into its 16th year. After the attacks on the Pentagon and World Trade Centre in 2001, the United States sent in troops to oust the Taliban government because it sheltered the operation's mastermind, Osama bin Laden. At a Senate hearing in June, Mattis acknowledged, "We are not winning in Afghanistan right now".