Mattis, the former commander of all Middle East wars, said on Tuesday that the USA is not winning the war in Afghanistan.
Mattis defended the US sacrifice in Afghanistan as preventing enemies from launching external attacks and said the new approach would bring more diplomatic and intelligence and, crucially, air support.
Earlier on Wednesday, Mattis testified at a US Senate hearing and said senior officials were outlining a new US strategy for Afghanistan.
There are now about 8,400 U.S. troops devoted to Operation Resolute Support in Afghanistan, which encompasses both United States counter terrorism forces to fight ISIS and the Taliban as well as the effort to train, advise and assist Afghan forces in a separate effort.
Mattis, who first rose to national prominence in 2001 as the one-star general who led an amphibious task force of Marines that carried out the raid on Kandahar province in Afghanistan, has promised to "correct" the situation there.
As for strategy, Mattis said the administration's war approach is being developed in a broader context that includes Afghanistan's neighbors, Iran and Pakistan, as well as India.
The defense secretary added that he would be able to brief Congress on the details of the new Afghanistan policy within weeks.
The Arizona senator's latest comments come a day after he excoriated Defense Secretary James Mattis at a hearing for not yet presenting a strategy from the Trump administration on Afghanistan. Our overall mission Afghanistan remains the same.
"I believe that we pulled out forces at a time, as you know, when the violence was lower, but we pulled them out on a timeline rather than consistent with the maturation of the government and the security forces", he said.
Mattis says this does not reflect any change in military strategy for the 16-year war.
There are now about 8,500 USA troops in Afghanistan and around 5,000 forces from additional nations in the North Atlantic Treaty Organization.
"Does Mattis do something different, or fall into the trap of the last eight years of doing the same thing but doing it better?"
Roughly 8,400 US troops are already serving in Afghanistan.
The US now has some 8,400 troops in Afghanistan. US and coalition air support for Afghan military operations against the Taliban diminished as the USA drew down its forces and ended combat operations there in late 2014.
"If all we are doing is tinkering around at the margin of a strategy that amounts to 'Muddle through and hope for a miracle, ' then 3,000 to 5,000 troops are not going to make a difference", Stephen Biddle, a professor at George Washington University and an Afghanistan expert, told AFP. Additional conversations must be had if the Pentagon decides it needs a few thousand more additional troops in coming years, he said.
The new troops, if deployed, would "provide more fire and air support to the Afghans". A former USA official said such a decision might allow the White House to argue that it was not micromanaging as much as the administration of former President Barack Obama was sometimes accused of doing.