A 22-year-old man has been charged by the US authorities over Saturday's shooting in Arizona, in which a congresswoman was seriously injured and six people died, the BBC reported.

Federal prosecutors charged Jared Loughner with trying to assassinate the US Democratic Representative Gabrielle Giffords, 40, and killing two other government officials. He is due to appear in court and he could face death penalty.

A total of 14 people were injured and six people, including a federal judge and a 9-year-old girl, were among the dead.

Giffords was hospitalized in critical condition. She underwent a surgery for a single gunshot wound to the head. Doctors have said they were "cautiously optimistic" about her recovery.

The attack happened about 10 minutes after the start of a previously scheduled public meeting outside a grocery store in Tucson, Arizona when a man holding a gun moved towards the crowd and opened fire.

Local Sheriff Clarence Dupnik said that a woman, who was waiting to have her photograph taken with the congresswoman, tackled the gunman as he tried to reload his gun.

She grabbed the bottom of the suspect's weapon but he managed to reload. However, the gun malfunctioned and two men then restrained him.

Dupkin said that they had prevented a much greater tragedy.

The police have searched Loughnber's home and have found an envelope with messages saying "I planned ahead","my assassination" and the name of Giffords.

The man was charged with two counts of first-degree murder for the killings of the two federal judges, John Roll and Gabe Zimmerman. He was also charged with attempted assassination over the shooting of the congresswoman and two other aides of hers.

US state authorities are also expected to bring charges against him later for attacking non-governmental employees.

The man who was believed to have been involved in the attack was cleared on Sunday, Dupnik said.

Loughner has been described by various classmates as "obviously disturbed," the BBC reports. He was said to be a loner who had posted a number of anti-government videos and messages on social networking websites.

Shortly before the attack, he posted the following message: "Goodbye friends. Dear friends, don't be mad at me."