Washington - US Defence Secretary Leon Panetta will lift a ban on women serving in combat, officials said on Wednesday - a ground-breaking move after a decade of war that saw female troops thrust onto the battlefield.
The decision marks yet another sweeping change for the US military under President Barack Obama, who led a drive to end a prohibition on openly gay troops.
Panetta and General Martin Dempsey, the chairperson of the US Joint Chiefs of Staff, "are expected to announce the lifting of the direct combat exclusion rule for women in the military", one official, who spoke on condition of anonymity, told reporters.
"This policy change will initiate a process whereby the services will develop plans to implement this decision, which was made by the Secretary of Defence upon the recommendation of the Joint Chiefs of Staff," the official said in an email.
Panetta and Dempsey were set to officially announce the move, which would open up hundreds of thousands of combat posts to women, on Thursday, officials said.
Under the decision, the armed services will have until January 2016 to carry out the changes.
Democratic lawmaker Tammy Duckworth, a former Black Hawk helicopter pilot who lost both her legs in the Iraq war, hailed the change.
Upper body strength
"America's daughters are just as capable of defending liberty as her sons. Lifting the ban on women in combat is good for our nation," Duckworth said in a tweet.
While women have been allowed to fly combat aircraft and fire weapons on naval ships, the Pentagon had retained restrictions on women serving in ground combat units.
In February last year, Panetta opened up about 14 000 combat-related jobs to women in an incremental step that was criticised as timid by some activists.
Calls to lift the blanket prohibition have mounted after more than 10 years of war in which women fought and died in counter-insurgency campaigns in Iraq and Afghanistan where front lines were blurred.
Some senior officers have privately voiced concerns that infantry and special forces units require major upper body strength and that difficult physical tests should not be relaxed for female recruits.
And right-leaning commentators have questioned whether mothers in uniform - especially single parents - should be sent into combat, even if they volunteered for service.
204 000 women in active duty
The Marine Corps recently opened up infantry officer training to women but the two females who volunteered failed to pass the gruelling test.
Female veterans and activists say they are only demanding an equal chance to apply for combat jobs - and not any special treatment.
US commanders began taking a second look at the ban in 2010 to reflect the changing reality on the battlefield, as the wars in Iraq and Afghanistan have put women in harm's way in any case.
Women make up about 14.5% of the active duty US military, or about 204 000 service members, according to the Pentagon. And advocates for changing the policy have long argued that denying female troops a chance at combat jobs effectively blocks them from attaining top jobs as commanders.
The 1990-91 Gulf war sparked an earlier wave of reform, paving the way for women to serve in fighter jets, attack helicopters and naval warships.
Panetta's decision would apply mainly to the Army and the Marine Corps, as the Air Force and Navy already have lifted most prohibitions on women in combat. In 2010, the Navy opted to allow women to serve on submarines.
The combat exclusion policy adopted in 1994 bars women from being assigned to ground combat units, but female troops have found themselves in battlefield situations by serving in units that are "attached" to ground units.
Lawmakers in Congress and rights groups welcomed the decision.
"After two wars over 10 years in which our enemies did not recognise a clear 'front', it is appropriate that we recognise the realities of modern military combat," Senator Mark Warner of Virginia said in a statement.
The American Civil Liberties Union said it was "thrilled" and that the policy change meant "qualified women will have the same chance to distinguish themselves in combat as their brothers-in-arms, which they actually already have been doing with valour and distinction".