http://therealnews.com/t/index.php?option=com_content&task=view&id=31&Itemid=74&jumival=3832&updaterx=2009-06-09+00%3A57%3A47
Apparently (second hand news -- I don't have audio at work) police opened fire on protesters with live ammo. The protesters didn't take too kindly to that, and fought back.
The issue is that agreements with the US and Canada would open up new parts of the Peruvian Amazon to be cleared to make way for mining/whatever.