DENVER -- A column of people three blocks long, led by members of the Iraq Veterans Against the War, marched from a Rage Against the Machine Concert at the Denver Coliseum to the Pepsi Center, where the Democratic National Convention was being held.

They marched to the so-called Freedom Cage -- a fenced-in free speech area just outside the Pepsi Center where police had designated as a safe protest zone.

"We are the veterans! The Iraq War veterans! The anti-war veterans!" they chanted along the 4-mile trek. "We are soldiers! Anti-war soldiers!"

Crowd estimates, generally around 4,000, were fluid as the group lost and picked up people along the way.

Marine Corps staff Sgt Jeff Key said he planned to deliver a one-page letter to Democratic presidential candidate Barack Obama.

Iraq Veterans Against the War wanted Obama to agree to an immediate withdrawal of troops from Iraq. They also want full health care benefits for returning troops and veterans, and reparations to the Iraqi people for damage caused by the war.

The group pledged to conduct a sit-in at the convention site until their message was heard.

Tensions mounted as police officers in riot gear multiplied in numbers in front of the security entrance to the Pepsi Center.

Key urged supporters to remain cooperative with Denver Police, “who’ve been exceptional,” he said.

Negotiations continued until, just before 8 p.m., when Key said that he and another member of the Iraq Veterans Against the War will meet with an Obama staffer to make sure their message is heard.

The crowd eruputed in cheers and hugged one another.

"It makes me think (Obama) actually cares," said an unidentified woman wearing a military uniform.

"As long we're still moving forward and participating in our democracy, that's success; that's what success looks like," Key told a large group of reporters and photographers.

Earlier in the day about 9,000 people attended a free concert at the coliseum, where a reunited Rage Against the Machine performed.

Although there was a large police presence early on, one observer noted a less-threatening tone -- from a LED sign on the vehicle leading marchers that read, 'Follow Us,' and 'Welcome to Denver,' to officers without riot gear riding along the route on mountain bikes.

Dozens of veterans, some in uniform, began the march in formation, chanting "She Wore a Yellow Ribbon."

People on motorcycles and bicycles joined those on foot. Some people held signs that said "U.S. out of Iraq" with red handprints and "No War on Iran." A few had the numbers of lawyers written on their bodies in case they were arrested.

Behind the veterans, protesters yelled: "Troops out now!"

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.

Jonny 5, Brer Rabbit and Andy Guerrero of the Denver group Flobots were with the marchers, as was Raymond "Boots" Riley of political hip-hop group The Coup, who also performed at the concert.

Emily Stewart from Philadelphia said the concert carried a non-violent theme.

"All of the messages from the performers and the people who spoke in between the performances were about peace and love," Stewart said.

Lindsay Mauro, 20, of Fort Collins, carried a sign that said, "I like Boys, Not Bombs." She decided to join the march when she heard about it at the concert.

"I definitely support (the protest), I have a lot of friends in Iraq," she said.

Employees of businesses along march route watched the protesters.

"It was scary at first, but they're just marching. They're trying to be Americans, I guess," said Sylvester Williams, a Navy veteran from the Vietnam War. "I was part of Vietnam and that was a hoax. This Iraq (expletive) is even worse."

Jack Scott watched the marchers quietly.

"It's pretty neat, we can still do this in this country," he said.

Protest organizers repeatedly urged the crowd to stay peaceful. Anyone willing to be arrested at the Pepsi Center sit-in was directed to find a place near the front of the march line.

Protesters were told by organizers not to react to the police presence or risk getting hit with pepper spray.

There were rumors of protesters carrying bottles filled with urine, but organizers urged marchers to maintain the peace since the primary goal was to have their message heard.

"We need to vote with our feet in the street and make our message loud enough for the whole world to hear," said anti-war protester Noel Juan.

"We want our troops home now. We want them taken care of when they get here. The America I know would not torture anybody," said Trish Gallagher with Code Pink, an organization that advocates peace.

The march included several protest groups

Critchfield said the veterans' group is committed to being nonviolent, but they'll be arrested if they have to.

With temperatures in the 80s, at least one business along the march route was selling juice, and several people could be seen stepping out of line to get one of the drinks before rejoining the crowd.

About 8,000 free tickets were handed out by lottery for the concert, sponsored by Tent State University and Iraq Veterans Against the War.

Rage Against the Machine also plans a concert Sept. 3 in Minneapolis during the Republican National Convention, which takes place just across the Mississippi River in St. Paul.