DENVER - Thousands of anti-war demonstrators converged near security gates outside the Democratic National Convention hall on Wednesday, chanting slogans and asking to talk to party officials about getting U.S. troops out of Iraq.

Police in riot gear ordered the group to disperse, and after about 15 minutes many protesters drifted off. But about 400 gathered several blocks away, still within sight of the Pepsi Center, where the Democrats nominated Barack Obama for president.

The protesters wanted to give Obama a letter asking that he agree to an immediate withdrawal of troops from Iraq, provide full health care benefits for returning troops and veterans and provide reparations to the Iraqi people for damage caused by the war.

The protest began with an anti-war concert by Rage Against the Machine and other groups, which drew about 9,000 people to the Denver Coliseum. Afterward, throngs began the 6.5-kilometre march toward the Pepsi Center.

The veterans, some in uniform, began the march in formation, chanting "She Wore a Yellow Ribbon," a song used as a marching cadence.

As marchers went past a line of police officers about three blocks from the Pepsi Center, they shouted: "Tell me what democracy looks like. This is what democracy looks like."

Jan Critchfield, 24, of Seattle said he served in Iraq in 2004, and after returning home, came to believe that the war was an "unlawful, immoral occupation."

He said now that he's back in the U.S., he thinks about what it's like for Iraqis living with U.S. forces in their country.

"I just can't imagine driving through my neighborhood at home and seeing a security checkpoint."

Critchfield said he joined the army at 17 without much thought about the implications.