AMMAN - US Defence Secretary Jim Mattis confirmed Sunday that the Trump administration had decided on a new strategy for Afghanistan after "rigorous" debate, but said President Donald Trump would be the one to announce it.

Mattis refused to hint at any details of the decision, which came after months of speculation over whether Trump, frustrated with a stalemate after 16 years in Afghanistan, would allow the Pentagon to boost troop numbers on the ground in the country.

However Mattis appeared satisfied after what he described as an in-depth review of the policy by much of the president's cabinet and top security officials at Camp David on Friday.

"I'm very comfortable that the strategic process was sufficiently rigorous, and did not go in with a preset condition in terms of what questions could be asked and what decisions could be made," he said.

"Everyone who had equity was heard," he said, including budget officials responsible for funding the effort.

Trump had several options on the table that ranged from backing away from the country to stepping up US efforts to defeat the Taliban. In June he gave Mattis the power to increase troop numbers above the estimated 8,400 that have been in the country - close to 4,000 more, according to reports.

But Mattis said he was loathe to move before he had a true picture of the numbers, which he said were actually higher than 8,400, and before Trump had his say on the broader strategy.

"The president had to make strategic decisions," Mattis said. "He delegated to me, when he came in, the tactical and operational decision. He did not delegate one ounce of the strategic decision."

"He really did come in with very different courses of action, and I think he now needs the weekend to collect his thoughts about how he's going to explain it to the American people."

Mattis said he is satisfied with how the administration formulated its new Afghanistan war strategy. But he refused to talk about the new policy until it was disclosed by President Trump.

Mattis did not mention that Genenral Joseph Votel, who as Central Command chief is responsible for directing the war in Afghanistan, was not invited to the Camp David talks. Votel has said his views were represented by Mattis. The top US commander on the ground in Afghanistan, Gen John Nicholson, also was not invited to attend.

Trump wrote on Twitter on Saturday that he had made decisions at Camp David, "including on Afghanistan," but he did not say more about it. The expectation had been that he would agree to a modest boost in the US war effort with an additional 3,800 to 3,900 troops.

Mattis said Trump had been presented with multiple options. He did not name them, but others have said one option was to pull out of Afghanistan entirely. Another, which Mattis had mentioned recently in Washington, was to hire private contractors to perform some of the US military's duties.

Pulling out American forces "would be a total failure," Colonel Abdul Mahfuz, the Afghan intelligence agency chief for Qarahbagh, north of Kabul, said Saturday. And he said that substituting paid contractors for US troops would be a formula for continuing the war, rather than completing it.

Mattis arrived in Jordan Sunday on the first day of a five-day swing through the Middle East and Eastern Europe. In Jordan he will meet with King Abdullah on regional security matters.

In Turkey he will hold discussions with President Recep Tayyip Erdogan and top military officials focused on the Syria conflict and the fight against the Islamic State group.

In Ukraine he will discuss US support for the country's military fighting pro-Moscow rebels and attend celebrations for the country's national day.