Sarah Palin at centre of storm over political vitriol after spree leaves six dead and congresswoman in critical condition

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.