Secretary of Defense Leon Panetta has decided to lift a ban that prohibited women from serving in combat, a congressional source tells NPR's Tom Bowman. The move opens up thousands of front-line positions.

Panetta is expected to announce the decision along with the Chairman of the Joint Chiefs of Staff on Thursday.

Citing "senior defense officials," the AP adds:

"The groundbreaking move recommended by the Joint Chiefs of Staff overturns a 1994 rule banning women from being assigned to smaller ground combat units. Panetta's decision gives the military services until January 2016 to seek special exceptions if they believe any positions must remain closed to women."

Back in November, four servicewomen along with the American Civil Liberties Union sued the Pentagon and Panetta over the combat exclusion policy.

Women, the lawsuit claimed, were already serving in combat roles, but were not receiving recognition for it. The ACLU said the combat exclusion kept women from more than 200,000 positions.

Perhaps a prelude, last year, the military opened 14,500 positions to women and lifted a rule that prohibited women from living with combat units.

Citing a "senior defense official," CNN reports the change won't happen immediately.

CNN explains:

"The Army and Marine Corps, especially, will be examining physical standards and gender-neutral accommodations within combat units. Every 90 days, the service chiefs will have to report back on their progress."The move will be one of the last significant policy decisions made by Panetta, who is expected to leave in mid-February. It is not clear where former Sen. Chuck Hagel, the nominated replacement, stands, but officials say he has been apprised of Panetta's coming announcement."'It will take awhile to work out the mechanics in some cases. We expect some jobs to open quickly, by the end of this year. Others, like Special Operations Forces and Infantry, may take longer,' a senior defense official explains. Panetta is setting the goal of January 2016 for all assessments to be complete and women integrated as much as possible."

This story is breaking. We'll update this post with reaction and more details, so make sure to refresh this page.

Update at 5:20 p.m. ET. 'Fantastic News':

Carey Lohrenz, a former Navy Lieutenant and one of the first women to fly F-14s on air craft carriers, tells our Newscast unit that this is "fantastic news," but it's really just catching up with the reality on the ground.

"We have women in combat roles right now. We are just not able to promote them," she said. "They're on the ground in Iraq; they're on the ground in Afghanistan. This is strictly formalizing and recognizing what their contributions currently are."

Sen. Mazie K. Hirono, a Democratic member of the Armed Services Committee from Hawaii, said the move was a "great step toward equality."

"I know that the women who currently serve in the military think they should be treated the same as any other servicemember," Hirono said in a statement. "Women serving in combat roles will strengthen our national security, and as a member of the Armed Services Committee, I will work closely with military and administration officials to see this change through."

Update at 4:14 p.m. ET. Infantry Troops:

As we alluded to earlier, the implementation of this new policy will be complex. The Wall Street Journal adds an important caveat saying that while this is the "largest expansion yet of women in combat roles," "defense officials said they don't expect the change to result in women being allowed to serve as infantry troops."

Copyright 2016 NPR. To see more, visit http://www.npr.org/.