The demonstrations come days after General David Petraeus, the senior US commander in Iraq, testified to the US congress on conditions in Iraq.
Viviana Hurtado, Al Jazeera's correspondent in Washington DC, said the anti-war demonstration was attended by people from a wide variety of backgrounds.
"One of the differences with this demonstration is that it is being led by Iraqi war veterans," she said.
Many of those who took part in the march were veterans of Iraq. Phil Aliff, 21, marched as a member of Iraq Veterans Against the War.
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"I stayed [in Iraq] for a year, in Abu Ghraib and outside Fallujah," he said.
"When we arrived, we were told we were here to bring stabilisation to the country.
"But we were not rebuilding anything. The Iraqis had only two hours of electricity. And I saw the atrocities committed by the Americans there."
Hurtado said that a 'die-in', a protest where people would lie motionless in front of the US Capitol, was the main focus of the anti-war demonstration.
"At least 1,000 people are hoping to symbolise US and Iraqi deaths [in Iraq] at the US Capitol," she said prior to the 'die-in'.
At least 160 people were arrested after they scaled a barricade at the foot of the Capitol steps during the symbolic protest, the Associated Press later reported.
Those who jumped the waist-high barrier gave themselves up calmly but the police used chemical spray on at least two people, the agency reported.
Relatives of soldiers who are serving or had served in Iraq were a key group within the public demonstration.
Diane Santoriello held a photograph of her son Neil, who was killed in Iraq in August 2004.
"I am here to get Congress to de-fund the war," she said. Brian Becker from the Answer (Act Now to Stop War and End Racism) coalition, the group organising the anti-war march, said Iraqi civilians wanted US forces out of their country.
"The vast majority of the people in the US want the war ended and the troops brought home now," he said.
Speakers at the anti-war demonstration included Cindy Sheehan, an activist who son was killed while serving in Iraq.
US public support for the war is at an all-time low, with 62 per cent of Americans believing that the war was a mistake, according to a New York Times/CBS poll published last week.
Public trust in both the Bush administration and congress to end the war is much lower than in military commanders, the poll results showed.