Enrique Pena Nieto was officially inaugurated in Mexico City shortly after midnight and took the oath of office before the Mexican Congress later in the day.
Fox News said at least 60 people were arrested for smashing windows in hotels, buildings and restaurants in the city's center Saturday as Pena delivered a speech inside the National Palace. Protesters also sprayed graffiti on statues and monuments. Police used tear gas during several skirmishes with protesters who were throwing rocks
"We've never had a provocation like this in the city," Mayor Marcelo Ebrard said at a news conference. "We reject totally and absolutely these barbarous acts."
The New York Times reported Pena, 46, has cast his image as the face of a new version of the Institutional Revolutionary Party (PRI) that would be more responsive to the public than when it governed Mexico for much of the 20th century. He campaigned on a platform that included continued cooperation with the United States on the economy and anti-narcotics programs.
But Pena received only 38 percent of the popular vote, which the Los Angeles Times said would likely make it tough to implement the government reforms he promised on the campaign trail.
In particular, Pena may have alienated powerful PRI governors and the labor unions that have provided the party with support over the years. The Los Angeles Times said his proposal to open up Mexico's nationalized oil industry to foreign investment was likely to face resistance from the oil workers unions.