Obamas lead silence for shooting victims

US President Barack Obama and First Lady Michelle Obama have bowed their heads in a moment of silence for the victims of the Arizona shooting.

Around 300 members of the White House staff joined the Obamas at the brief outdoor ceremony on a frigid day in Washington.

Two US Marine guards opened the White House doors for the Obamas to emerge. After walking several paces toward the lawn, they stood beside each other with somber expressions on their faces. A Marine honour guardsman standing on a balcony rang a bell three times and, a minute later, the Obamas returned inside in silence.

Jared Lee Loughner, 22, is facing charges for the shooting of Representative Gabrielle Giffords and 19 other people - six of whom were killed - in Tucson on Saturday.

Loughner has been charged with two counts of first degree murder, one count of attempted assassination of a member of Congress and two other counts of attempted murder. Prosecutors say other charges could be filed.

Two patients have been discharged from hospital. Two more remain in the intensive care unit. Five are in a serious condition.

Giffords is said to be in a critical condition after a single bullet travelled the length of her brain on the left side, hitting an area that controls speech. Given the devastating wound, doctors said they were uncertain about the extent of brain damage she may have suffered.

US federal judge John Roll and a nine-year-old girl were among the six people killed, while 14 others were wounded.

Investigators said in the charges against Loughner that they found an envelope at his residence with the handwritten phrases "I planned ahead" and "My assassination," along with the name "Giffords" and what appeared to be his signature.