US Defence Secretary Leon Panetta has decided to lift the military's ban on women serving in combat, a senior Pentagon official has said.

The move could open hundreds of thousands of front-line positions and elite commando jobs to women.

It overturns a 1994 rule prohibiting women from being assigned to small ground-combat units.

But the military would have until 2016 to argue for any specific posts they think should remained closed to women.

The decision is expected to be formally announced on Thursday.