Hope as Giffords smiles from her hospital bed

The husband of shot US congresswoman Gabrielle Giffords says his wife's condition has improved so much that she has been able to smile and give him a neck rub at her hospital bedside.

The interactions with astronaut Mark Kelly are new signs of the Arizona Democrat's impressive progress in recovering from the assassination attempt which happened as she held an open-air meeting on January 8.

The mass shooting outside a Tucson supermarket left six dead and 13 others wounded, including Ms Giffords, who was shot in the head.

But Ms Giffords (40) still cannot speak because of a tube in her throat that is helping her breathe.

"She's in the [intensive care unit]. You know, gone through this traumatic injury. And she spent 10 minutes giving me a neck massage," Mr Kelly said.

"It's so typical of her that no matter how bad the situation might be for her, you know, she's looking out for other people."

Such encounters indicate higher levels of functioning, implying that "she's recognising him and interacting, perhaps in an old familiar way with him", said Dr Michael Lemole.

Mr Kelly has also been essential in helping Ms Giffords' staff through the tragedy, said Mark Kimble, a Tucson staff member who stood only a few feet from the politician when she was shot.

"There is not a doubt in his mind and not a doubt in any of our minds that she's going to be back.

"He's been cheering us up. He'll come over and when we're down, he'll say, 'Gabby's going to make it, Gabby's a little better today'. That's a big help to all of us."

The shooting suspect, 22-year-old Jared Loughner, remains behind bars in Phoenix.