Mexico's presidential campaign season has officially ended, with the candidates calling on voters to head to the polls on Sunday, be vigilant and bring about change in a country that wants to go in a different direction.

The three-month campaign was marked by extensive political advertising, rallies across the country and numerous promises by candidates ahead of an election that, if the polls are correct, will have a clear winner.

Frontrunner Enrique Peña Nieto, of the Institutional Revolutionary Party, or PRI, ended his campaign Wednesday in Toluca, a city in central Mexico that is a bastion of his party.

"We are ahead in all the polls, but we cannot allow ourselves to let our guard down. This is the time to redouble our efforts," the 45-year-old candidate said.

The PRI, which governed Mexico from 1929 to 2000, is trying to regain the presidency after coming up short in the past two elections.

"We are four days away from winning the presidency of the republic," Peña Nieto said, adding that Mexico needed "responsible change."

Andres Manuel Lopez Obrador, candidate of the leftist Progressive Movement coalition, also cited the need for change, telling tens of thousands of supporters at a rally in Mexico City's Zocalo plaza that he would win.

"The people want real change and they will not be able to prevent it with dirty wars or by buying loyalties, consciences and votes," Lopez Obrador said.

The former Mexico City mayor, who is running No. 2 in the polls, told his supporters that he campaigned hard so he "can again win the presidency of the republic."

Lopez Obrador lost the 2006 presidential election to Felipe Calderon, of the conservative National Action Party, or PAN, by 0.56 percent and has never recognized the results.

Josefina Vazquez Mota, of the PAN, said that if she won on Sunday, she would ask Calderon, who made the war on Mexico's drug cartels the centerpiece of his administration, to serve as her attorney general.

"I want an attorney (general) for the nation who is not an accomplice of crime," Vazquez Mota said during a rally at Estadio Omnilife in Zapopan, a city in the western state of Jalisco.

Peña Nieto and Lopez Obrador are two faces of an old system, Vazquez Mota said.

Peña Nieto represents "authoritarianism, abuse of power and surrender to crime," the PAN candidate said, adding that Lopez Obrador was the "face of chaos and economic crisis."

Presidential longshot Gabriel Quadri, of the New Alliance Party, or PANAL, ended his campaign in Zacatecas, saying that he wanted Mexicans living in the United States to return home, create businesses and spur development.

Mexico will hold its presidential election next Sunday, selecting a successor to President Felipe Calderon.

Nearly 80 million Mexicans will be eligible to vote for a new president, 628 legislators and thousands of other officials in the general elections. EFE