PRESIDENT BARACK OBAMA and his first lady, Michelle, have led a moment’s silence in tribute to the six victims of Saturday’s shooting in Tuscon, Arizona.

In the South Lawn of the White House, Obama led hundreds of staffers in observing the silence as flags were lowered to half-mast in honour of the victims.

Also present was French president Nicolas Sarkozy, who continued with a scheduled visit to Washington despite the developments.

“Obviously all of us are still grieving and in shock from the tragedy that took place,” Obama said afterward. “Right now the main thing we’re doing is offering our thoughts and prayers to those who have been impacted.”

ABC News reports that the Supreme Court also observed the moment’s silence, in memory of Judge John Roll, chief judge of the US District Court of Arizona, who was killed in Saturday’s shooting.

The court had begun hearing its arguments in today’s business ten minutes early, so as to make time for the silence at 11am.

Gabrielle Giffords, the congresswoman who was the target of the shooting, remains in a critical condition, but doctors this afternoon said they were optimistic about her condition.

Giffords had been hosting a ‘Congress on your Corner’ event when Jared Lee Loughner, 22, opened fire.

Loughner is to face two counts of murdering employees of the federal government, two counts of attempted murder on federal government employees, and charges for the attempted murder of Congresswoman Giffords, when the district court convenes at 9am Irish time tonight.

He could face the death penalty if found guilty.

The Daily Telegraph quotes FBI director Robert Mueller, who said other charges may also be put to Loughner.

The US House of Representatives has decided to delay debate on a motion that would repeal Obama’s flagship healthcare bill, set for Wednesday, in efforts to diffuse the political tension arising from the shootings; instead, it will pass a resolution honouring the victims of the shooting.