Gabrielle Giffords was the intended target, Sheriff Clarence Dupnik said
A US congresswoman is in critical condition after a gunman shot her in the head and killed six people in an Arizona shooting spree.
Democratic Representative Gabrielle Giffords was shot at close range at a public meeting in a Tucson supermarket.
The 40-year-old is under sedation, but the doctor treating her said he was “very optimistic about her recovery”.
Barack Obama said the shooting was a “tragedy for our entire country”. A 22-year-old man has been arrested.
He has been named locally as Arizona resident Jared Loughner, who is described as having a troubled past.
He is described by various former classmates as “obviously disturbed” and a loner who had posted a number of anti-government videos and messages on social networking websites.
“It is an indication of the febrile, volatile nature of politics in America that, immediately the news broke, the internet was alive with anger, a dispute between the left and the right”
Local police, who have not confirmed the suspect’s name, said they were hunting for a possible accomplice, who may have driven the suspect to the supermarket.
“We’re not convinced that he acted alone,” said Pima County Sheriff Clarence Dupnik.
Police have released a CCTV image of the person they are hunting, described as a white man aged between 40 and 50 with dark hair who was wearing a blue jacket and jeans at the time of the attack.
Left-wing commentators have accused right-wing politicians of creating a climate of hatred that allows such attacks.
The rhetoric that instantly sprang up around the shootings shows the volatile, febrile state of American politics, says BBC North America Editor Mark Mardell in Washington.
Sheriff Dupnik said a consuming atmosphere of political vitriol centred on Arizona may have been a factor in the attack.
“When you look at unbalanced people, how they respond to the vitriol that comes out of certain mouths about tearing down the government,” he said.
“The anger, the hatred, the bigotry that goes on in this country is getting to be outrageous. And unfortunately, Arizona, I think, has become the capital. We have become the Mecca for prejudice and bigotry.”
This anger had spilled into violence before, with Ms Giffords’ office being vandalised last March after she upset Arizona conservatives by supporting Mr Obama’s healthcare reform bill.
Former Alaska Governor Sarah Palin, a conservative Republican, had placed Ms Giffords on a list of politicians she wanted to remove from office in mid-term elections last November.
As a moderate Democrat who narrowly defeated a so-called tea party candidate in November’s mid-term elections, Ms Giffords had referred to the hatred during an interview with MSNBC.
“We’re on Sarah Palin’s targeted list, but the thing is, that the way that she has it depicted has the crosshairs of a gun sight over our district. When people do that, they have to realize that there are consequences to that action,” she said.
Mrs Palin has issued a statement offering her condolences to the families of Ms Giffords and the other victims of the attack.
The attacker struck as Ms Giffords held one of her regular open-invitation meetings – which she called “Congress on your corner” – with her constituents outside the Safeway supermarket in Tucson at around 1000 (1700GMT) on Saturday.
Eyewitnesses say the gunman approached Ms Giffords and shot her at close range. Later reports from the hospital said a bullet passed through her head without exploding.
The attacker then fired some 20 shots indiscriminately before being overpowered by members of the crowd as he attempted to reload what one witness described as a semi-automatic Glock pistol.
He was then hauled away by police, witnesses said.
The six dead included a nine-year-old girl, federal Judge John Roll – who had spent more than 40 years on the bench – and one of Ms Giffords’ political aides.
In addition to the six deaths, police said 13 people – including Ms Giffords – had been wounded.
Mr Obama urged the nation to “come together, and support each other”.
The suspect has been described as a loner “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”, and tasked FBI director Robert Mueller with overseeing the investigation.
Ms Giffords, who represents the eighth district of Arizona in the House of Representatives, is married to space shuttle astronaut Mark Kelly.
Described as a “a rising star” in the Democrats with hopes of eventually winning the Arizona Senate seat, 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.
The House of Representatives majority leader Eric Cantor announced that all of next week’s legislative debates would be postponed to allow politicians to “take whatever actions may be necessary in light of today’s tragedy”.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.