PITTSBURGH, September 25 (RIA Novosti) - Police used tear gas to disperse an unauthorized march of protesters against a summit of the Group of Twenty richest nations in Pittsburgh, Pennsylvania, a RIA Novosti correspondent reported on Friday.

Several hundred protesters gathered near the center of the city, and when police attempted to stop their march they started rolling trash bins toward police officers and even threw rocks at a police car.

Police responded with firing tear gas canisters at the protesters. Some of the demonstrators were seen coughing and scratching their eyes.

A police official told RIA Novosti reporter that the protesters refused to obey police requests to stop and turned violent.

"After several warnings we used smoke grenades and horns [to disperse the crowd]," the official said.

He refused to provide any more details on the incident.

RIA Novosti has not yet obtained any commentary from the city authorities.

The G20 summit on September 24-25 focuses on steps to overcome the global economic crisis.