The U.S. military has overturned a requirement for its troops to be in contact with enemy forces in Afghanistan before opening fire in a bid to relax the rules of engagement and defeat the Taliban.

Defense Secretary Jim Mattis approved the change following President Donald Trump’s pledge in August, during a policy speech on Afghanistan, to “lift restrictions and expand authorities” regarding U.S. operations in the central Asian nation.

”We will also expand authorities for American armed forces to target the terrorists and criminal networks that sow violence and chaos throughout Afghanistan,” Trump said at the time.

On Tuesday, Mattis told two congressional panels that the White House gave him the authority to repeal certain requirements for troops in Afghanistan in order to accelerate the fight against the terrorists, the Military Times reported.

The changes include removing proximity requirements for strikes against the Taliban and extending U.S. advisers to lower-level Afghan units.

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President Donald Trump speaks at Fort Myer in Arlington Va., Monday, Aug. 21, 2017, during a Presidential Address to the Nation about a strategy he believes will best position the U.S. to eventually declare victory in Afghanistan. (AP)

“You see some of the results of releasing our military from, for example, a proximity requirement — how close was the enemy to the Afghan or the U.S.-advised special forces,” Mattis told the Senate Armed Services Committee, the Military Times reported. “That is no longer the case, for example. So these kind of restrictions that did not allow us to employ the airpower fully have been removed, yes.”

Mattis also confirmed the changes at a later hearing, saying, “We are no longer bound by the need for proximity to our forces. It used to be we have to basically be in contact with that enemy.”

As for deploying U.S. advisers among the Afghan units, Mattis said local troops in Afghanistan are typically more successful in batltle when assisted by NATO or U.S. advisers.

“Those units with NATO and American advisers win, and those without them often do not win,” he said. “So we are going to spread the number of units with advisers to bring that air support to win.”

The changes do not mean Afghanistan's civilian population will no longer be protected, Mattis said, stressing that U.S. soldiers will do everything “humanly possible” to avoid civilian deaths.

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U.S. Secretary of Defence Jim Mattis leaves a news conference after a NATO defence ministers meeting at the Alliance headquarters in Brussels, Belgium June 29, 2017 (Reuters)