He made the remarks at a hearing with members of the Senate Armed Services Committee yesterday, chaired by Senator John McCain who criticised the Trump regime for not coming up with a policy for Afghanistan despite being in office for six months.
"I think Taliban had a good last year and they're trying to have a good one this year, sir. I think we may be able to, by a change in some of our concepts of operations, help them with air support and fire support. That'll put the enemy on the back foot. Right now, I believe that the enemy is surging, right now," Mattis said.
"We're now six months into this administration, we still haven't got a strategy for Afghanistan. It makes it hard for us to support you when we don't have a strategy. We know what the strategy was for the last eight years, don't lose. That hasn't worked," he said.
"The sacrifice of these heroes is a painful reminder that America is still a nation at war. That is true in Afghanistan where, after 15 years of war, we face a stalemate and urgently need a change in strategy, and an increase in resources if we are to turn the situation around," he said.
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"I believe by mid-July we will be out to brief you in detail. We are putting it together now and there are actions being taken to make certain that we don't pay a price for the delay. But we recognise the need for urgency and your criticism is fair," he said.
"We are not winning in Afghanistan right now. We will correct this as soon as possible. I believe the three things we are asking for stand on their own merit, however, as we look more broadly at the protection of the country. But that in no way does that relieve me of the need to deliver that strategy to you," he added.
"...The Afghan government has got a degree of integrity in what it is contributing to its people -- the government services. The corruption has been driven down. But, most of all, that the Taliban no longer has the freedom of movement that we're seeing right now that has been rolled back," he said.
Mattis also pitched for allying with Afghan forces to fight against the extremists.
"I think one of the ways that we get after that is by more effectively assisting them, both in planning operations and delivering combined arms, most specifically the aviation capabilities.
Three US soldiers were killed and another wounded on Saturday when they were attacked by an Afghan soldiers, who was then killed.
Two US Army Rangers died in a April 27 raid on an IS compound in eastern Afghanistan. Officials were investigating whether they were killed by friendly fire in the opening minutes of the three-hour battle.
Their deaths came just days after a US Army special forces soldier was also killed in the region.