|Loughner is facing five charges including the attempted murder of Gabrielle Giffords, a US congresswoman [Reuters]
Jared Loughner, the suspect in the shooting rampage that killed six people over the weekend, has been brought to court on five federal charges.
The 22-year-old faces separate murder and attempted murder charges over the incident on Saturday in Tucson in the state of Arizona that left more than a dozen wounded.
Loughner told the judge he understood the charges against him but made no statement.
Al Jazeera's Rosiland Jordan reporting from Washington said Loughner was ordered held without bail and will be assigned Judy Clarke as his defence lawyer.
"She has defended among others Zacarias Moussaoui, the 20th hijacker in the September 11, 2001, attacks, Timothy McVeigh in the Oklahoma City bombings case in 1995 and Theodore Kaczynski, better known as the Unabomber, in the US mail bombings.
"If convicted Loughner could be executed both under the federal and state court systems. It remains unclear when he would be tried for the killings," added our correspondent.
Meanwhile, Barack Obama, the US president, led the nation in a moment of silence in honour of the victims of a weekend shooting in Arizona that left six dead and a congresswoman seriously wounded.
Flags were at half-mast at the White House and the Capitol, where the steps of the US congress were crammed with politicians paying tribute to the victims.
Obama and his wife Michelle emerged from the White House at 11am local time (1600 GMT), took a few steps onto the South Lawn and stood, heads bowed, as a bell was rung.
Officials said Obama will be travelling to Arizona on Wednesday to attend a memorial service for the shooting victims.
Giffords, 40, who represents Arizona's eighth congressional district in the House of Representatives, is said to be doing well in hospital after being shot in the head during the attack in Tucson.
Doctors said on Monday that she was still responding to simple commands and her condition is stable.
Her brain remains swollen, but the pressure has not increased.
Six people, including a US federal judge and a nine-year-old girl, were killed in Saturday's attack, with Giffords and 13 others wounded.
Eight of those injured remain hospitalised.
Following an acrimonious campaign in the run-up to last November's midterm congressional elections, some commentators were quick to cite a shrill climate of political vitriol might have played a role in the shooting.
"We are in a dark place in this country right now and the atmospheric condition is toxic," Cleaver told NBC's Meet the Press.
The suspected attacker opened fire with a semi-automatic pistol at point-blank range outside a supermarket.
Police seeking a motive for the shooting spree were looking at a trail of anti-government messages on the internet left either by Loughner or someone writing under that name.
There was no coherent theme to the messages.
In Tucson, Clarence Dupnik, the Pima County sheriff, said the suspect had made threats to kill in the past but not against Giffords.
Obama has put Robert Mueller, the FBI director, in charge of the investigation.