Hundreds of anti-NATO protesters marched through the streets of Chicago Saturday demanding the release of three activists arrested on terror charges.

The crowd chanted "our passion, our freedom, is stronger than their prisons" as it blocked traffic in the central business district before making its way to within blocks of the heavily-guarded lakefront convention center where the leaders of more than 50 countries will be meeting from Sunday.

One protester was arrested after getting into a confrontation with a policewoman riding a bike, in what was an otherwise cheerful and peaceful march.

People chanted "this is a peaceful protest" as the crowd began to bristle at the confrontation which was eventually subdued.

Authorities charged three men Saturday with plotting to attack President Barack Obama's campaign headquarters and other targets during the two-day NATO summit which opens Sunday.

Prosecutors told reporters that the men had gathered an arsenal of weapons -- including Molotov cocktails, throwing stars, gas masks, knives, a hunting bow, brass knuckles and a shield with protruding nails -- and also spoke of their desire to acquire assault rifles.

They planned to destroy police cars and attack four police stations -- including police headquarters, state attorney Anita Alvarez added.

Some of the other proposed targets included the home of Chicago mayor Rahm Emmanuel and "certain downtown financial institutions," she said.

But protesters insisted that the three men who hail from Florida, New Hampshire and Massachusetts were framed.