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(CNN) -- Enrique Pena Nieto was sworn in as Mexico's new president Saturday, returning his party to power and promising to change the country's fight against organized crime.
Pena Nieto belongs to the Institutional Revolutionary Party (PRI), which ruled Mexico for more than 70 years before losing the presidency in 2000.
"We are a nation that is going at two different speeds. There's a Mexico of progress and development. But there's another, too, that lives in the past and in poverty," he said during his inaugural address at the National Palace in Mexico City.
"Mexico has not achieved the advances its people demand and deserve," he said.
Pena Nieto, 46, promised to create economic opportunities and reduce violence. Peace, he said, would be his government's first goal.
More than 60,000 people lost their lives in drug-related violence during the six-year term of his predecessor, Felipe Calderon.
Without jobs and social programs, Pena Nieto has said, millions of people will turn to crime.
Pena Nieto said earlier this week that his security strategy will focus on reducing the drug-related violence, though he provided few specifics about how he would stem the violence or what aspects of Calderon's strategy he will change.
The two men took part in handover ceremonies.
Exactly as scheduled, at 12:01 a.m. local time, Calderon and Pena Nieto walked down the escalators to a patio in the National Palace.
In a ceremony lasting about five minutes, Calderon received the national flag from a military school cadet and immediately handed it to Pena Nieto. The act symbolized the transfer of command of the security forces.
Afterward, both men greeted members of the new Cabinet, then the outgoing Cabinet members.
Minutes later, in a separate ceremony, Pena Nieto conducted the oath of office of the new Security Cabinet, comprised of Miguel Angel Osorio Chong as the head of the Ministry of the Interior, Salvador Cienfuegos Zepeda as head of the Ministry of National Defense and Vidal Soberon Sanz as Secretary of the Navy.
Pena Nieto said the new government had taken office "from the first minute of this day."
"A governmental transition has been completed in an orderly, legal and transparent fashion," he said.
"This process has helped to preserve the political stability, economic and social development of the nation. Mexico has shown democratic maturity and institutional strength," he said. "In accordance with Article 83 of the constitution, today I begin to exercise the honorable position of president of the United States of Mexico."
As Pena Nieto was being sworn in, his opponents clashed with police outside Congress. Video showed protesters hurling rocks at metal barriers, as police fired back with tear gas.
Pena Nieto won 38% of the vote in July, besting his closest competitor, Andres Manuel Lopez Obrador, who garnered some 32% of the vote and refused to accept the result.
Pena Nieto and Calderon took to social media to commemorate the transition.
"My term ends, but not my commitment to Mexico, which I will continue fighting until the last of my days," Calderon tweeted.
Another of his tweets read: "The handover of the national flag for the change of guard from the president to the president-elect symbolizes the transfer of command."
Calderon is headed next to Harvard University's John F. Kennedy School of Government in Cambridge, Massachusetts. The school announced this week that Calderon will spend the next year as a global public leaders fellow at the school.
Pena Nieto tweeted: "Starting today, I begin to occupy the post of Constitutional President of the United Mexican States. I am confident in my team and I recognize their track record, which supports its commitment to Mexico."
CNN's Nelson Quinones contributed to this report.