The US was tonight seized by a fierce debate over whether inflammatory rightwing rhetoric was to blame for a shooting spree in Tucson, Arizona, that targeted congresswoman Gabrielle Giffords and left six dead, including a nine-year-old child.

Giffords, 40, who remains critically ill in hospital after being shot through the head but is expected to live, criticised Sarah Palin last year for putting her and 19 other Democrats on a hitlist of districts, each shown as being in crosshairs.

"When people do that, they have got to realise there are consequences to that action," Giffords said. Palin today distanced herself from the shooting, as did leading figures of the Tea Party movement. Conservative bloggers accused liberals of seeking to exploit the attack.

Barack Obama called on Americans to hold a moment of silence at 11am today to commemorate the victims of the shooting and he spoke of the attack as a national tragedy, and promised to get to the bottom of it. "A suspect is currently in custody, but we don't yet know what provoked this unspeakable act." He described Giffords as a friend. "It's not surprising that today Gabby was doing what she always does – listening to the hopes and concerns of her neighbours. That is the essence of what our democracy is all about. That is why this is more than a tragedy for those involved. It is a tragedy for Arizona and a tragedy for our entire country."

The US department of justice said the suspect, Jared Lee Loughner, 22, had been charged with five criminal counts, including attempted assassination of a US congresswoman. Loughner is expected to appear in federal court in Phoenix today before a federal magistrate judge.

Robert Mueller, the FBI director, said the attack was "not only against dedicated public servants but against citizens, one a child. This was an attack on our institutions and an attack on our way of life."

The National Jewish Democratic Council – Giffords is the first Jewish woman elected to Congress from Arizona – saw the attack as emanating from the polarised political debate: "It is fair to say – in today's political climate, and given today's political rhetoric – that many have contributed to the building levels of vitriol in our political discourse that have surely contributed to the atmosphere in which this event transpired."

Giffords's father was blunter. Asked if she had any enemies, he said: "Yeah, the whole Tea Party."

Giffords, a former Republican turned Democrat, had been holding a public meeting in a shopping mall when the gunman opened fire.

Loughner is described by the authorities as mentally unstable. He is alleged to have used a semi-automatic pistol, bought in November. The dead included a federal judge, a nine-year-old girl and a Democratic party worker. Police have not identified a motive and Loughner has opted to remain silent.

A second man captured on a security camera with Loughner near the scene of the attack has been cleared of involvement, police said.

Repeated questions about the bitterness of the debate were raised last year during the election, with fears for Obama's life and those of other leading Democrats as a result of repeated questioning about his eligibility to be president and the constitutionality of his acts. The fear was that fringe groups not committted to the peaceful political process might be influenced by the wilder outbursts of right-wing politicians and commentators.

James Clyburn, one of the Democratic leaders in the House, calledtoday for political rhetoric to be toned down. "We're living in a time that all of us should begin to take stock of how our words affect people, especially those who aren't very stable."

The sheriff conducting the investigation, Clarence Dupnik, did not mince his words. "When you look at unbalanced people, how they respond to the vitriol that comes out of certain mouths about tearing down the government – 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."

When Giffords held a similar meeting last year, someone dropped a gun. In March, a window at her office was shattered, possibly by an airgun pellet.

Palin, on a website, targeted Giffords and 19 other Democrats in symbolic crosshairs. By this evening, the site had been removed. Palin, on Facebook, expressed her condolences. A Palin aide, Rebecca Mansour, speaking on the Tammy Bruce radio talkshow, denied the symbol represented crosshairs. "We never ever, ever intended it to be gun sights," Mansour said.

Palin is well-known for her intemperate language and actions, including her recent call for the WikiLeaks founder Julian Assange, to be hunted down, and the crosshairs incident has the potential to hurt her in this year's jockeying for the Republican presidential nomination.

Giffords, in an interview with MSNBC in March last year, said: "We are on Sarah Palin's targeted list. The way that she has it depicted has the crosshairs of the gunsight over our district."

The former senator and Democratic presidential hopeful Gary Hart, writing on the Huffington Post website, blamed symbols such as crosshairs and the use of words such as "targeted".

"Today we have seen the results of this rhetoric," Hart wrote.

The Tea Party movement sought to establish a clear gap between it and the shootings. Amy Kremer, chair of the California-based Tea Party Express, said: "Spirited debate is desirable, but it only should be the clash of ideas. An attack on anyone for political purposes, if that was a factor in this shooting, is an attack on the democratic process. We join with everyone in vociferously condemning it."

Conservative commentator Erick Erickson criticised liberals on his blog Red State for "subtly and not so subtly pinning the blame for the attempted assassination of the congresswoman and the related shootings on the Tea Party movement, Sarah Palin, Rush Limbaugh, Glenn Beck, me, you, and everyone right of centre".

Pete King the Republican Congressman, echoed this: "The best way to avoid politicizing it is to not make a political issue out of it. It's a horrible tragedy. From what we know it's a deranged person, and I think any other discussion at this time does politicise it."

The new Speaker of the House, John Boehner, today confirmed that controversial legislation scheduled for this week is to be postponed, including proposed repeal of Barack Obama's healthcare reform, the single issue with which Giffords was most passionately associated. He called for a security review: "I have also asked that the Sergeant at Arms, US Capitol Police, and FBI conduct an in-depth security overview for members on Wednesday. I'm also directing the Sergeant-at-Arms and Capitol Police to conduct a bipartisan security briefing for district directors."