Image caption Ms Giffords, an Arizona Democrat, was shot at a constituency meeting

US Congresswoman Gabrielle Giffords, shot in the head in an Arizona attack, is walking and stringing sentences together, doctors in Texas say.

Ms Giffords' condition was said to be improving in "leaps and bounds".

Doctors also said her husband and medics had told her about the shooting that wounded 13 and killed six people.

Doctors said it was too early to say whether she would be able to attend the launch of the Space Shuttle mission to be commanded by her husband in April.

On Wednesday, Jared Loughner, 22, pleaded not guilty to 49 new charges, relating to the attack at Ms Giffords' constituency event in Tucson on 8 January.

Most of the charges Mr Loughner currently faces relate to the killing of a federal employee; use of a firearm to commit a violent crime, cause injury or death; and injuring or causing death to participants at a federally protected activity

If convicted, he could face the death penalty.

Ms Giffords' husband Mark Kelly, an astronaut, has resumed training as commander for the final flight of the space shuttle Endeavour, scheduled for April. He had withdrawn from the training programme when his wife was shot.

Doctors told a news conference on Friday that Ms Giffords was speaking in full sentences, such as "I'm tired and want to go to bed".

"I'm very happy to report that she's making leaps and bounds in terms of neurological recovery," Dr Dong Kim said.

Dr Kim said that while Ms Giffords did not remember the shooting, she had been told about the event both by her husband and by medical staff.

"She's very upbeat, focused on getting better. She hasn't shown us depression and she's just been very forward looking and even with the speech she's not showing much frustration," Dr Kim added.