Reporters Without Borders says it is unclear what prompted police to step up their level of force during a demonstration that began outside the Pepsi Center on the opening night of the convention.

"We understand the security issues surrounding the Democratic National Convention but we urge the Denver police and other law enforcement authorities to show restraint toward journalists covering demonstrations and not be an obstacle to the news gathering process," Reports Without Borders said.

Officers were observed trying to prevent photographers from recording the incidents.

USA Today videographer Garrett Hubbard was one of the people identified as being roughed up by police as he tried to film the demonstration from a sidewalk.