MEXICO CITY Enrique Peña Nieto assumed the presidency of Mexico on Saturday amid high hopes that his once-autocratic political party, which governed this country for most of the 20th century, will heal a bruised, bloodied nation and rev the economy.

Peña Nieto, 46, donned the red, white and green presidential sash shortly before noon in front of a raucous Congress and turmoil in city streets.

Near Congress and in front of historic Alameda Park, protesters opposed to Peña Nieto threw rocks and bottles at riot police, set fire to a bank branch, smashed windows of a hotel and numerous other storefronts and ran from a cascade of tear gas. An undetermined number were injured.

The moment marked a chaotic return to power for the Institutional Revolutionary Party, or PRI, which was ousted at the ballot box in 2000 after 71 years of near absolute rule.

Peña Nieto, a telegenic former governor of Mexico state, persuaded voters in July 1 elections that a revived PRI had abandoned its old, autocratic practices and would undo some of its policies of decades past, such as blocking foreign investment in the oil sector, in a bid to bring greater prosperity to Latin America’s second-largest economy.

He hit upon those same themes in his first speech as president, delivered at the ornate National Palace before hundreds of Mexican dignitaries and foreign heads of state and envoys, including Vice President Joe Biden.

“Mexico has not achieved the advances that its people demand and deserve,” Peña Nieto said. “Insecurity and violence have robbed the peace and freedoms of diverse communities in our territory.”

He outlined programs to alleviate poverty and hunger, protect single mothers and the elderly and build new infrastructure, such as a passenger train system.

“We are a nation that grows at two speeds. There is a Mexico of progress and development. But there is also one that lives in backwardness and poverty,” he said.

He only talked obliquely about the drug-related turmoil that has wracked Mexico over the past six years. Crime gangs engaged in beheadings, mass slaughters and firefights for smuggling routes have left a horrendous toll: More than 60,000 people – perhaps far more – have died in bloodshed since late 2006.

Yet Peña Nieto appeared determined to de-emphasize the fight against crime and focus more intensely on economic growth, which only recently has picked up after a lackluster decade.

If Peña Nieto is successful, the impact will ripple to the United States, where 6 million jobs depend on exports to Mexico.

Fears that the party has not changed were palpable. Full page newspaper ads lamented the “death to democracy” in Mexico and lambasted the PRI for “buying” the July 1 election with the support of Televisa, a huge television and media conglomerate.

The second-place finisher, Andres Manuel Lopez Obrador, led a rally of thousands of protesters at the iconic Angel of Independence monument, where a banner referred to Peña Nieto: “Mexico hates you.”

Early in the day, bottle-throwing protesters tried to breach security barriers outside Congress before Peña Nieto’s arrival. Youths ripped down street-side payphones, tore up pavement and commandeered a garbage truck, ramming it against a tall steel security fence. Small fires burned from Molotov cocktails.

Police said seven protesters were injured in the morning. They denied reports that one man died from head injuries after a homemade bottle rocket struck him. No tally was offered for afternoon violence.

Inside the chamber, leftist lawmakers unfurled a huge black and white banner and held up giant placards decrying Peña Nieto’s inauguration. “Mexico in Mourning,” the banner said. “Teleprompter president, No Need to Assemble,” another said.

Despite the unruly scenes, the inauguration proceeded far more smoothly than in 2006, when months of street blockades and political turmoil followed a hotly contested presidential race that saw the National Action Party and its then-leader Felipe Calderon barely edge out Lopez Obrador.