Clashes outside Mexico's Congress as it begins opening session

ROUGH CUT (NO REPORTER NARRATION)

STORY: Student groups clashed with police in Mexico City on Sunday as hundreds of demonstrators attempted to block Congress to keep lawmakers from entering for their opening session.

Clouds of tear gas filled the street in front of Congress as riot police advanced on the protesters.

The young people, who came largely from the anti-government group "I am 132", covered their faces and shouted slogans such as: "Not one more step back" and "Out with Pena Nieto", referring to Mexico's President Enrique Pena Nieto.

They threw rocks, sticks and Molotov cocktails as they tried to block Congress, which was guarded by hundreds of federal police officers.

Initial reports said that two police officers were injured and taken to the hospital.