Mexico RIOTS over new President.

MEXICO CITY (AP) — Enrique Pena Nieto has taken the oath of office as Mexico's new president, bringing the old ruling party back to power after a 12-year hiatus.

His Institutional Revolutionary Party ruled for 71 years with a mix of populist handouts, graft and rigged elections before being voted out and replaced by the conservative National Action Party in 2000.

Pena Nieto has promised to govern democratically with transparency.

A demonstrator lights up a spray outside the steel security barriers around the National Congress, where the swearing in of new Mexican President Enrique Pena Nieto took place. / Marco Ugarte, AP

His swearing in was marred Saturday by protesters outside the Congress lobbing homemade bombs and firecrackers and shouting: "Mexico without the PRI!"

Before the swearing in, leftist congressmen inside the chambers demanded to know what was going on in the crowds and urged police to use restraint. Congressman Rafael Huerta of the Labor Party urged the new government to protect the people.

The street where Mexico's Congress is located is shown blocked by a metal barricade in Mexico City, Monday, Nov. 26, 2012. Police heightened security around the building where Mexico's President-elect Enrique Pena Nieto, of the Institutional Revolutionary Party (PRI) will be sworn-in on Dec. 1.