Photos of a smiling but visibly altered Gabrielle Giffords have been posted on her Facebook page, the first images of the US congresswoman released since she was shot in the head in January.

Ms Giffords smiles broadly in one of the two pictures, dated 17 May. The second photograph shows her seated next to her mother Gloria Giffords.

Both pictures, released by Giffords's congressional campaign, were taken the day before the Arizona representative underwent surgery to replace part of her skull.

No pictures of her post-surgery have been released.

The photos were intended to show how far Ms Giffords has come since being shot at point-blank range on 8 January outside a supermarket near Tucson, Arizona where she was meeting constituents.

‘These photos reveal an upbeat image of Gabrielle Giffords,’ her spokeswoman CJ Karamargin said.

‘When you see the pictures you see that she has progressed in leaps and bounds. When they say that a picture is worth a thousand words, if ever that was true, it is true here.’

Her chief of staff Pia Carusone told the Arizona Republic last week that although Giffords seems to understand what is said to her, she still has trouble speaking in complete sentences and expressing complex ideas.

Six people, including a federal judge and a nine-year-old girl, were killed and 12 others wounded in the shooting spree.

In March, the alleged shooter, Jared Loughner, was declared mentally unfit to stand trial.

Experts found the 22-year-old to be schizophrenic and unable to help in his own defence or understand court proceedings.

US media reports said Ms Giffords would soon leave the Houston hospital where she has been receiving rehabilitation treatment and would continue to receive outpatient therapy at home.