Police say a Houston-area woman fatally shot her two adult daughters before officers shot and killed her.

The incident happened about 5 p.m. Friday in front of a home on the fringe of the Houston suburb of Fulshear. Fort Bend County Sheriff Troy Nehls says a motive was still under investigation, but it appeared the shooting climaxed a family argument.

Nehls says the two younger women had already been shot when a Fulshear police officer arrived and saw the mother with a gun in her hand, apparently preparing to shoot one of her daughters again. The officer shot and killed the woman.

No identities have been released.