Enrique Pena Nieto sworn in as Mexico's new president

MEXICO CITY - Enrique Pena Nieto was sworn in as Mexico's new president Saturday for a six-year term, marking the return to power of the once long-ruling Institutional Revolutionary Party (PRI).

Pena took the oath of office at the traditional venue in the capital Mexico City, the San Lazaro Palace Chamber of Deputies, amid the tightest security ever to surround a transition of power in recent history.

Mexico's new President Enrique Pena Nieto waves after taking oath in congress in Mexico City December 1, 2012. Enrique Pena Nieto took over as Mexican president on Saturday, offering a shot at redemption for the party that shaped modern Mexico if he can bring an end to years of violence and economic underperformance. [Photo/Agencies]

"I vow to safeguard the Constitution ... and fulfill the office of the Presidency, which the people have conferred on me," Pena said, addressing an assembly of 479 deputies and 123 senators, and several guests, including U.S. Vice President Joe Biden, Spain's Prince Felipe and Canadian Governor General David Johnston.

Immediately after taking the oath, he received the presidential sash from outgoing President Felipe Calderon, of the National Action Party (PAN).

The Mexico's 66th president is expected to address the nation from the National Palace shortly after his swearing in.

Prior to the ceremony, representatives of the country's seven political parties assembled in the chamber to make speeches, as customary.

Opposition legislators carried placards critical of both the outgoing and incoming leaders. They unfurled a wall-sized banner with crosses and the words "Imposition Complete, Mexico in Mourning," in reference to the tens of thousands of victims of the war on drugs, the overriding legacy of outgoing President Calderon.

Outside the chamber, protestors lobbed rocks and molotocv cocktails at nine-foot-high metal barricades that had been erected days ago for several blocks around the venue. At one point, the demonstrators even tried to knock down the barricades with a truck, TV news said.

Police repelled protesters with tear gas and rubber bullets. One protester was allegedly killed by a bullet, TV added.

In a move designed to head off any major clashes on inauguration day, Calderon and Pena Nieto held a brief 30-minute handover of power ceremony late Friday at the National Palace, attended by a small number of guests, members of the diplomatic corps and others.

Just past midnight, Pena received the "insignia of Federal Executive Power" from Calderon, the national daily La Jornada reported.

Immediately afterwards, Pena swore in several members of his new cabinet, all in the area of security, including the ministers of the Interior, National Defense and Navy, and the Deputy Minister of Security.

Pena won the presidential election last July 1 with 38.21 percent of the votes, marking an end to 12 years of PAN rule.