05/20/2012 12:22 pm ET Updated May 21, 2012

Chicago NATO Protesters, Police Clash Downtown (VIDEO)

Footage captured on the ground in downtown Chicago depicts high tensions and frequent clashes between protesters and police during NATO summit demonstrations, including several incidents that devolve into violence.

Video released by NBC Chicago shows one protester, then several trying to impede a police van's movement with their bodies, then being pushed down the street when the vehicle continues moving forward.

(See videos above, below.)

In a more recent video, protesters are confronted by police in riot gear, and several altercations between officers and demonstrators appear to turn violent.

Police say 18 people have been arrested over the past week, according to CBS Chicago. Not included in that count are four people arrested on suspicions of two separate terrorist plots who had plans to use Molotov cocktails during the summit, according to police.



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