Discuss as:

Protesters clash with police ahead of NATO summit in Chicago

Shawn Thew / EPA

Anti-NATO protesters fight with Chicago mounted police during an unpermitted march through Chicago streets. This was the sixth day of protests prior to the NATO Summit which runs May 20-21.

Related story: Attacks on Chicago police stations, Obama office were planned, prosecutors say

Eric Thayer / Reuters

Demonstrators clash with law enforcement officers during a protest.

Scott Olson / Getty Images

Demonstrators try to break through police lines as they march through the downtown streets of Chicago, Ill., May 19.

Three men were charged with conspiring to commit acts of terrorism at high-profile locations in Illinois ahead of the NATO summit. NBC's Kristen Welker reports.