A US congresswoman has been shot in the head and six other people have been killed by a gunman in Arizona.
Democratic Representative Gabrielle Giffords, 40, was shot at close range during a public meeting in Tucson.
She is in a critical condition, but the doctor treating her said he was "very optimistic about her recovery".
The dead included a nine-year-old girl and a federal judge. President Barack Obama said the shooting was a "tragedy for our entire country".
The Associated Press news agency reported that one of Ms Giffords' political aides was also killed in the shooting.
Police said a total of 13 people were shot and wounded during the attack. Doctors said five of them including Ms Giffords were in a critical condition.
A suspect named in local media as 22-year-old Arizona resident Jared Loughner was arrested after the incident.
Local police, who have not confirmed the suspect's name, said they were not convinced that the gunman was working alone.There is some reason to believe that he came to this location with another individual," said Pima County Sheriff Clarence Dupnik.
He said police were trying to trace the other person, who he said might have been involved.
Presidential tributeOne witness said he arrived at the scene of the shooting and initially thought he had heard sounds of hammering."But as I turned the corner I saw people running, the shutters were coming down over the pharmacy so I ran up to the front and you just saw people on the ground," Ken Penner told US broadcaster ABC.
"There was a lady coming in completely covered in blood, bullet holes in the windows where Giffords was standing."
The gunman was reportedly overpowered by a local security guard, before being taken away by police.
The dead judge was named by officials as John Roll, who had spend more than 40 year on the federal bench. It is not thought that he was deliberately targeted.
Mr Obama urged the nation to "come together, and support each other".
"I ask all Americans to join me and Michelle in keeping all the victims and their families, including Gabby, in our thoughts and prayers," he said.
He described Ms Giffords as a personal friend and an "extraordinary public servant".
Mr Obama has tasked FBI director Robert Mueller with overseeing the investigation.
'Rising star'Ms Giffords, who represents the eighth district of Arizona in the House of Representatives, is married to space shuttle astronaut Mark Kelly.She has served on several congressional committees, including those covering the armed services and foreign affairs, and is a member of the "blue dog" group of centrist Democrats.
Jeff Rogers, chairman of the local Democrats, told the BBC that Ms Giffords was "a rising star" in the Democrats with hopes of eventually winning the Arizona Senate seat.
She upset Arizona conservatives by supporting Mr Obama's healthcare reform bill last year.
Former Alaska Governor Sarah Palin, a conservative Republican, placed Ms Giffords on a list of politicians she wanted to remove from office in mid-term elections last November.
Ms Palin has issued a statement offering her condolences to the families of Ms Giffords and the other victims of the attack.
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