lowed the same route almost 40 years ago, when America was divided by the Vietnam War.

At its height, and in spite of freezing weather conditions, as many as 10,000 people joined Saturday's protest. There were smaller demonstrations in other US cities, including Los Angeles, New York and San Diego. The conflict, which has killed more than 3,200 American soldiers, will enter its fifth year tomorrow.

In Washington, the marchers, bearing banners with messages such as "Illegal Combat" and "Peace through Strength", were confronted at several points by smaller groups of counter-demonstrators. A contingent of military veterans congregated close to the Vietnam Memorial on the Washington Mall after hearing rumours that protesters had plans to deface it.

After crossing the Potomac river headed toward the Pentagon, the marchers also confronted another group of counter-demonstrations near the Arlington Cemetery where slain soldiers are buried. "Go to hell traitors," one sign read. "You dishonour our dead on hallowed ground."

Among those addressing the crowds was Cindy Sheehan, who became famous in 2005 for camping outside the Texas ranch of President George Bush after her son was killed in Iraq.

"We're here in the shadow of the war machine," she said after the marchers reached a cordoned-off site in sight of the Pentagon.

"It's like being in the shadow of the death star. They take their death and destruction and they export it around the world. We need to shut it down. We want the people in the White House out of our house and arrested for crimes against humanity."

The event was organised by a group called Answer Coalition, which is associated with a political faction called the Party of Socialism and Liberation.

The march on the Pentagon in October 1967 marked the beginning of the end of America's war in Vietnam. "We didn't lose the war in Vietnam, we lost it right here on this same ground," said Larry Stimeling, a Vietnam veteran, who was standing on the National Mall. "It's the same thing now."

For some protesters in Washington, there was at least the feeling that there had already been a shift in the political atmosphere, with Donald Rumsfeld now gone from the Pentagon and the new Democrat majority challenging the strategy in Iraq.

"It's all moving in our direction, it's happening," Ed Ellis, a Vietnam veteran, said while attending a rally in Los Angeles. Suggesting that the US was at a "tipping point" in determining the next step in Iraq, he added: "The administration, their get-out-of-jail-free card, they don't get one any more."

But a labour activist from New York, Michael Letwin, warned demonstrators in Washington not to invest too much hope in the Democrats. "This is a bipartisan war,", he said. "The Democratic party cannot be trusted to end it."

With President Bush at Camp David all weekend, a White House spokesperson, Blair Jones, said only: "Our constitution guarantees the right to peacefully express one's views. The men and women in our military are fighting to bring the people of Iraq the same rights and freedoms."

The weekend of demonstrations began on Friday evening when a coalition of Christian groups staged a similar march from the National Cathedral in Washington to the White House. It ended with 200 arrests in front of the White House after protesters allegedly forced their way through police lines.