The US military on Thursday eased some restrictions on women soldiers, allowing them to serve in thousands of jobs that will bring them closer to combat, defense officials said.

The move reflects the increasing presence of women on the front lines during a decade of war and marks a milestone for the American military, which has lifted prohibitions on women's roles since the 1970s in incremental steps.

"The department plans tomorrow to open 14,000 jobs that previously had been closed to women in the military," a senior defense official told AFP.

"This is only the start," the official said on condition of anonymity. "It's conceivable in the future, after conducting more reviews, that more jobs will be open to women."

The changes, which will be officially unveiled on Thursday, mainly apply to the Army and Marine Corps, the official said. The Air Force and Navy have few remaining restrictions on female service members, after a 2010 decision that allowed women to serve on submarines.

Until now, female intelligence officers, signal officers and other specialists could not serve in battalions likely to face direct combat, but the new policy will allow women "more tactical opportunities" instead of being confined to brigade-level posts, the official said.

Defense Secretary Leon Panetta approved the policy change after receiving an internal report that looked at women's roles and the experience of a decade of war that thrust them into battle.

But the policy change stops short of a wholesale repeal of the ban on women in combat, including rules that bar women from serving in special forces.

Despite those rules, women increasingly found themselves in firefights in Iraq and Afghanistan in recent years as they took part in counter-insurgency campaigns with no clear front lines.

Officials described the new rules, not as a radical reform, but as an evolutionary step to revise policies that were out of touch with battlefield realities.

The Pentagon is due to formally inform Congress of the change later on Thursday, giving lawmakers a brief period to delay or block the measure before it takes effect.

Congress ordered a review of women's roles after an advisory panel, the Military Leadership Diversity Commission, urged rescinding remaining restrictions that have prevented women from serving in ground combat units.

The successful performance of female soldiers in the 1990-91 Gulf war helped prompt an earlier wave of reform that paved the way for women to serve in combat aircraft and naval warships.

Opponents of allowing women in ground combat argue that they lack the required physical strength, that their presence could prove disruptive to the "cohesion" of combat units and that mothers should not be placed in harm's way.

But retired officers, both male and female, and activists have long urged a complete repeal of the combat exclusion rule, arguing that the restriction holds back women from senior leadership positions by denying them tactical experience deemed crucial for promotion.

Only about six percent of all of the Army's general officers are females, even though women comprise about 15-17 percent of the force.

At least 144 women service members have been killed in war since the attacks of September 11, 2001, according to the Pentagon.

The policy change comes only months after the US military ended a ban on openly gay troops serving in uniform.