Protests begin ahead of NATO summit in Chicago (46 images)

A protester wears a mask as he demonstrates against NATO in front of U.S. President Barack Obama's 2012 campaign headquarters on May 17, 2012 in Chicago. The protest was held as part of weeklong demonstrations leading up to the NATO summit being held on May 20 and May 21 in Chicago. UPI/Brian Kersey

Protesters demonstrate against NATO in front of U.S. President Barack Obama's 2012 campaign headquarters on May 17, 2012 in Chicago. The protest was held as part of weeklong demonstrations leading up to the NATO summit being held on May 20 and May 21 in Chicago. UPI/Brian Kersey

A Protester holds up a sign during a demonstration against NATO in front of U.S. President Barack Obama's 2012 campaign headquarters on May 17, 2012 in Chicago. The protest was held as part of weeklong demonstrations leading up to the NATO summit being held on May 20 and May 21 in Chicago. UPI/Brian Kersey

Protesters stage a die-in as they demonstrate against NATO drone strikes in front of U.S. President Barack Obama's 2012 campaign headquarters on May 17, 2012 in Chicago. The protest was held as part of weeklong demonstrations leading up to the NATO summit being held on May 20 and May 21 in Chicago. UPI/Brian Kersey