Mattis said the Taliban were "surging" at the moment, something he said he meant to address.
"This ensures the department can facilitate our missions and nimbly align our commitment to the situation on the ground", Mattis said, adding that the essential US goals in Afghanistan remain unchanged: help Afghan combat forces gain the upper hand on the Taliban, and hunt and kill Islamic extremists affiliated with al-Qaida and the Islamic State.
Even adding several thousand more US troops would keep levels well below the estimated peak of 100,000 deployed to the country during the Obama administration, not including foreign forces.
The U.S. now has 8,400 troops in Afghanistan.
Sponsored Content - Download our Executive Briefing to learn how agency and industry experts are hoping to reduce insider threats.
US and coalition forces are working the support mission, and Afghan forces will receive the air support that was in short supply, the secretary said.
Obama in 2014 declared an end the USA and NATO-led combat operations in Afghanistan, and responsibilities were handed over to local forces. He added that the Trump administration is working on a comprehensive cyber defence strategy, but in the meantime the USA has enough understanding of Russia's cyber actions to defend against them.
Defense Secretary James Mattis was grilled before the Senate yesterday, with Sen. John McCain, an Arizona Republican who complained about the administration's failure to determine an Afghanistan strategy, saying it "makes it hard" for Congress to support the administration's war efforts.
Leaked images of iPhone 8 surface online
And below is a photo of the iPhone 8 frame alongside what we believe are frames for the iPhone 7s and iPhone 7s Plus. In turn, there have been conflicting reports surrounding Apple's plans for the Touch ID sensor.
Mattis said his new strategy, which will be finished in the coming weeks, will restore the "high ground" by restoring North Atlantic Treaty Organisation air forces to a position of dominance, the Examiner reported.
Earlier on Tuesday, Mattis told a congressional panel that the review will be completed in mid-July. All have political stakes in the outcome and Mattis spoke about the State Department putting diplomatic and economic pressure on these countries.
US generals have recently recommended adding as many as 5,000 troops.
The Pentagon had considered a request for roughly 3,000 more troops, mainly for training and advising.
The new troops, if deployed, would "provide more fire and air support to the Afghans". Download the latest podcast here.
"We're not winning in Afghanistan right now", Mattis said, adding: "We'll correct this as soon as possible".
"It's going to be an era of frequent skirmishing and it's going to require a change in our approach from the last several years if we're to get it to that position", Mr Mattis said.
The Islamic State of Iraq and Syria has established a branch in Afghanistan's Khorasan province, al-Qaida and other terrorist groups remain active inside Afghanistan, and the Taliban continue to pose a challenge to the democratically elected government there, the secretary noted.