A demonstrator sprays water over the face of another demonstrator after police released pepper gas during a protest prior to the start of the G20 Pittsburgh Summit in Pittsburgh, Pennsylvania September 24, 2009. REUTERS/Carlos Barria (UNITED STATES POLITICS CONFLICT BUSINESS)
An anti G-20 Summit protester covers his ears from an acoustic device used by police to disperse protestors in Pittsburgh, Pennsylvania. Police fired tear gas to disperse a group of masked anarchist protesters attempting to march on the venue of the Pittsburgh G20 summit Thursday. (AFP/Getty Images/Chris Hondros)
Demonstrators walk away from pepper gas released by police during a protest prior to the start of the G20 Pittsburgh Summit in Pittsburgh, Pennsylvania September 24, 2009. REUTERS/Carlos Barria (UNITED STATES POLITICS CONFLICT BUSINESS IMAGES OF THE DAY)
Police boats pass under Greenpeace activists as they rappell from a bridge with a banner denouncing climate change in Pittsburgh, Pennsylvania. Activists have promised an angry welcome for leaders of the G20 economies when they arrive in Pittsburgh, with anarchist factions threatening to march on the summit venue. (AFP/Getty Images/John Moor
A Greenpeace activist is arrested by police in Pittsburgh, Pennsylvania. Activists have promised an angry welcome for leaders of the G20 economies when they arrive in Pittsburgh, with anarchist factions threatening to march on the summit venue. (AFP/Paul J. Richards)
A policeman watches monks as they walk during a protest against the government of Myanmar, prior to the start of the G20 Pittsburgh Summit in Pittsburgh, Pennsylvania September 24, 2009. Leaders of the Group of 20 countries meet in Pittsburgh on Thursday and Friday, their third gathering since the collapse of investment bank Lehman Brothers a year ago and with their the focus now shifting from combating the worst recession since the 1930s to discussing how to prevent it happening again. REUTERS/Carlos Barria (UNITED STATES POLITICS CONFLICT RELIGION)
Pittsburgh police in riot gear redeploy after confrontations with protestors near the Strip District in Pittsburgh, Thursday Sept. 24, 2009. Hundreds of demonstrators marched in protest of the G20, which is expected to begin in Pittsburgh on Thursday. (AP Photo/Jacqueline Larma)
President Barack Obama and first lady Michelle Obama arrive at Pittsburgh International Airport in Coraopolis, Pa., Thursday, Sept. 24, 2009. He will be attending the G-20 Summit being held in Pittsburgh on Friday, Sept. 25. (AP Photo/Gene J. Puskar)
National Guard troops man a checkpoint into downtown Pittsburgh, Pennsylvania, near the site of the G20 summit. Police fired tear gas to disperse a group of masked anarchist protesters attempting to march on the venue of the Pittsburgh G20 summit Thursday. (AFP/Saul Loeb)
Demonstrators march in the Lawrenceville section in Pittsburgh, Thursday Sept. 24, 2009 in protest of the G20 summit, expected to begin Thursday in the city. (AP Photo/Matt Rourke)
Police officers block a street during a protest prior to the start of the G20 Pittsburgh Summit in Pittsburgh, Pennsylvania September 24, 2009. REUTERS/Carlos Barria (UNITED STATES POLITICS CONFLICT BUSINESS)
A demonstrator kicks a tear gas canister thrown by police during a protest before the start of the G20 Pittsburgh Summit in Pittsburgh, Pennsylvania September 24, 2009. REUTERS/Carlos Barria (UNITED STATES POLITICS CONFLICT BUSINESS)
Demonstrators run from pepper gas released by police during a protest prior to the start of the G20 Pittsburgh Summit in Pittsburgh, Pennsylvania September 24, 2009. REUTERS/Carlos Barria (UNITED STATES POLITICS CONFLICT BUSINESS)
A woman raises her fist as protesters march past her in the Lawrenceville section of Pittsburgh, Thursday Sept. 24, 2009. Demonstrators marched ahead of the G20 summit scheduled to begin in Pittsburgh Thursday. (AP Photo/Matt Rourke)
Signs are propped against a tree during a protest before the start of the G20 Pittsburgh Summit in Pittsburgh, Pennsylvania September 24, 2009. Police used pepper gas to disperse protesters at the Group of 20 summit in Pittsburgh on Thursday as about 2,000 people marched despite warnings that force would be used to end the demonstration. REUTERS/Eric Thayer (UNITED STATES POLITICS BUSINESS CONFLICT)