Presidential candidate Enrique Pena Nieto speaks to supporters at his party's headquarters in Mexico City, Mexico on July 2, 2012. /AP

Voters in Mexico have chosen to bring the country's once dominant political party back into power by electing Enrique Pena Nieto as their next president.

According to the preliminary results that still must be validated, Pena Nieto had 38 percent of Sunday's vote to beat former Mexico City mayor Andres Manuel Lopez Obrador, who had 31 percent. 

On Monday, U.S. President Barack Obama called Pena Nieto to congratulate him and offer U.S. support in meeting mutual goals.

Pena Nieto said in an address to his supporters that Mexicans have voted for a change in direction, but he vowed to keep pressure on drug cartels.

"The fight against crime will continue with a new strategy to reduce violence and protect the lives of Mexicans," he said. "Let it be clear, with organized crime there will be no pacts or truce."

Lopez Obrador said he was not ready to concede.

"We have to represent them as they deserve to be represented, the citizens that have confided in us," he said. "We will not, in any way, act in an irresponsible way, we will have all of the information. And when it is the right time, we will inform the people of Mexico about the result of this election."

Pena Nieto's Institutional Revolutionary Party (PRI) ruled Mexico for 71 years until 2000, when voters elected National Action Party (PAN) candidate Vicente Fox. Outgoing President Felipe Calderon, also from PAN, followed in 2006, but his tenure has been plagued by economic stagnation and rampant drug violence.

Calderon deployed the military to fight the drug cartels shortly after he took office. More than 50,000 people have been killed in drug violence since then.

The PAN candidate in this year's election, Josefina Vazquez Mota, finished third in the voting.

Some information for this report was provided by AP, AFP and Reuters.