Seven people had been arrested as of 2:30 p.m. Sunday, according to police. The circumstances of those arrests have not been released.
An Associated Press report indicated that police and protesters clashed during the middle of the parade. The protesters, dressed in black, allegedly surged toward police and threw objects at officers. Police fought back with batons.
The protesters ran away, but reconvened with the main crowd near the parade's end at Cermak and Michigan Avenue. Police beefed up security around that area -- and officers showed up in full riot gear.
Police say for the most part the NATO protests have been peaceful.
Chicago Police Supt. Garry McCarthy spoke from Grant Park before the rally began.
"You're seeing us facilitating peaceful protest, protecting people, providing for the public safety, while at the same time being intolerant of crimes being committed," Supt. McCarthy said.
The protesters had permits for Sunday's Grant Park rally and parade, which was expected to be the largest anti-NATO event during the Chicago NATO summits. Thousands of people were expected to attend the Grant Park rally and downtown march. Police estimate between 1,800 and 2,200 people are marching, but Occupy Chicago estimates a crowd between 3,000 and 5,000.
Dozens of world leaders are in town for the NATO summit, which is being held at McCormick Place on May 20 and 21. The first NATO session was called to order at 2:10 p.m., just minutes after the anti-NATO march stepped off at 2:05 p.m.
Veterans lead anti-NATO march to McCormick Place
The anti-NATO march was led by dozens of U.S. military veterans, mostly Army and Navy, who have served tours in Iraq and Afghanistan. Over the week, the vets have shared their stories of disenchantment about a mission they say changed from disarming a country, liberating a country and then occupying that country. They're in town to argue on an international stage that troops should be withdrawn from Afghanistan before 2014.
"For every house that we enter, if there weren't terrorists there before, there are now," Graham Clumpner said.
"The military values the mission over the lives of these soldiers who recognize a very legitimate moral dilemma," Brock McIntosh said.
Also, they want full mental health care benefits for veterans.
At the end of the parade route, veterans threw their NATO medals over the fence that the Secret Service put up as a perimeter around McCormick Place. Each of them spoke briefly.
"We don't want your medals, we want to give them back because these are dishonor to hold, we want to give them back because we stand in solidarity with the people of Afghanistan, Iraq and all victims of occupation around the world," Scott Kimball said earlier Sunday.
"As veterans we swore to protect. We are once again going to step out front, make ourselves vulnerable and represent the majority of the people in this country. And give our medals back," Jacob George said.
The veterans had hoped a NATO representative would meet the group and take the medals back as a symbol of recognition.
Dozens of groups feed into anti-NATO rally/march
Sunday's rally and march is organized by Coalition Against NATO/G8 Rally/March, but dozens of other groups are also joining, ranging from Occupy to individuals.
"We believe there is no more real usefulness for NATO. It is no longer a form of defensive role. NATO should be eliminated," Blaise Sewell, Occupy Chicago, said.
"So yesterday we saw a massive amount of people mobilizing on the streets and standing up for their rights and I think today we're gonna see that times ten," Lenny Bianchi, Veterans for Peace, said.
Protesters clash with police in unplanned marches
Sunday's planned rally and march follows one other permitted rally, which was held Friday in Daley Plaza by Nurses National United. That rally was peaceful.
However, since then there have been several impromptu marches that tied up downtown streets, including one Friday afternoon and one Saturday evening, which involved multiple arrests.
Supt. McCarthy spoke about an incident in which a protester was pushed by a police van on Saturday night. He said the officer was injured, suffering a concussion, but the protester was released from the hospital. Watch the Video
"The officer was at the front of the march and unfortunately the march overran him," Supt. McCarthy said. "This was one officer in a van by himself being swarmed by a crowd. Significant damage to the vehicle, his tires were slashed, the officer was injured. He had to get out of there. It's really that simple."