A small group of protester lock arms and stands in front of police lines on Liberty Avenue in Pittsburgh, Pennsylvania on September 24, 2009. Pittsburgh is the host city for the two day G20 Summit. UPI /Archie Carpenter | License Photo

Protesters rally in Arsenal Park, in the Lawrenceville area of Pittsburgh, Pennsylvania before attempting to march in the G20 Summit site on September 24, 2009. Pittsburgh is the host city for the two day G20 Summit of world leaders. UPI /Archie Carpenter | License Photo

A protester with his face hidden joins the march as it leaves Arsenal Park on its way to the G20 Summit in Pittsburgh, Pennsylvania on September 24, 2009. Pittsburgh is the host city for the two day G20 Summit of world leaders. UPI /Archie Carpenter | License Photo

A police lines forms on Penn Avenue to repel demonstrators outside of downtown Pittsburgh, Pennsylvania as they attempt to march to the location of the G20 summit in Pittsburgh, Pennsylvania on September 24, 2009. Pittsburgh is the host city for the two day G20 Conference. UPI /Archie Carpenter | License Photo

Three protester with his face hidden joins the march as it leaves Arsenal Park on its way to the G20 in Pittsburgh, Pennsylvania on September 24, 2009. Pittsburgh is the host city for the two day G20 Summit. UPI /Archie Carpenter | License Photo

A protester rolls a trash dumpster down Liberty Avenue into police lines in Pittsburgh, Pennsylvania on September 24, 2009. Pittsburgh is the host city for the two day G20 Conference. UPI /Archie Carpenter | License Photo

A group of protester rolls a trash dumpster down Liberty Avenue into police lines in Pittsburgh, Pennsylvania on September 24, 2009. Pittsburgh is the host city for the two day G20 Conference. UPI /Archie Carpenter | License Photo

Protesters regroup on Liberty Avenue in Pittsburgh, Pennsylvania before attempting to march in the G20 Summit site on September 24, 2009. Pittsburgh is the host city for the two day G20 Summit of world leaders. UPI /Archie Carpenter | License Photo

PITTSBURGH, Sept. 24 (UPI) -- Protests at the G20 economic summit turned violent at times Thursday with demonstrators throwing rocks and police firing rubber bullets, Pittsburgh police said.

Police used pepper spray and smoke canisters to break up a march in downtown Pittsburgh but some of the marchers began throwing rocks and police responded by firing rubber bullets, the Pittsburgh Post-Gazette reported. In a separate incident, police used gas canisters to disperse a crowd estimated at 500 -- many of them said to be curious onlookers -- near Phipps Conservatory, where heads of state were to have dinner, the newspaper said.


Vic Walczak, legal director for the local ACLU, said the crowd was peaceful and even moved when a police car needed to pass through.

"I don't think this is an unlawful assembly," he said.

The two-day summit began Thursday.

Fourteen Greenpeace activists were arrested Wednesday trying to scale city bridges. A Greenpeace spokesman said the activists were trying to send a "message to the leaders of the G20," the Pittsburgh Tribune-Review reported.

The arrests occurred after eight people rappelled from a bridge and unfurled a banner reading: "Danger. Climate Destruction Ahead. Reduce CO2 Emissions Now." Police said they also detained five people trying to hang a banner from the Fort Pitt Bridge.

Groups this week have protested Group of 20 economic policies, President Barack Obama's administration, a coal conference and other issues, the Tribune-Review reported.

To deal with an expected high number of demonstrators and protect security perimeters in Pittsburgh's downtown area, the city hired out-of-state officers and brought in several thousand state police troopers and Pennsylvania National Guard troops.