Mexico's presidential candidates are making a final push for votes ahead of the bitterly contested 2 July election.
Felipe Calderon launched a fierce attack on Mr Lopez Obrador
Conservative Felipe Calderon ended his campaign in Mexico City, saying his opponent would push Mexico into crisis.
Mr Calderon said Andres Manuel Lopez Obrador would plunge the country into a "horror movie" of debt and division.
Mr Lopez Obrador holds his final rally in the capital on Wednesday, ending a campaign marked by insults on all sides and amid rising violence and tensions.
Eleven people, including four police officers, were killed over the weekend in the southern state of Guerrero, officials said.
The bodies of the officers, who were seized by armed men on Wednesday, were found bound and riddled with bullets, the officials said. A police spokesman said a drug gang was believed to be behind the killings.
Police also found seven bodies in three different locations in the Pacific resort of Acapulco, which is in Guerrero state, on Sunday, just hours before Mr Lopez Obrador was due to hold a rally there.
72m registered to vote
Mexicans abroad can vote for first time
President elected for 6 years
Elections also for Chamber of Deputies, Senate, 3 state governors, Mexico City mayor
The authorities said there was no indication that the killings were connected to the campaign but they were the latest in a series of execution-style murders in the resort.
Drug violence and attacks on police have risen ahead of the poll. Last week, three police officers and a civilian were beheaded in Tijuana on the US border.
All five of the candidates have promised to tackle crime.
Addressing a crowd of 100,000 in Mexico City's Azteca Stadium, Mr Calderon launched a fierce attack on Mr Lopez Obrador.
The latest opinion polls suggest the two men are running almost neck-and-neck but there are a lot of undecided voters.
Candidates have been criss-crossing the country
"Our adversaries represent an alternative of hate and slander," said Mr Calderon, the candidate of President Vicente Fox's National Action Party (PAN).
His project was for a Mexico "of growth, economic stability and employment", while Mr Lopez Obrador would bring "inflation, devaluation and economic crisis", Mr Calderon told the cheering crowd.
"We've seen this movie before and it was a horror movie that all Mexicans paid for dearly."
Mr Lopez Obrador, a former mayor of Mexico City and candidate of the leftist Party of the Democratic Revolution (PRD), is due to end his campaign in Mexico City's main square on Wednesday.
He has rejected accusations that he could undermine Mexico's economic stability.
"We are not going to commit any abuses, we're not going to take away anyone's goods, he said at a rally last Thursday.
Electoral rules require all candidates to stop campaigning to allow a period of reflection before the vote on Sunday.
Also standing are Roberto Madrazo of the Institutional Revolutionary Party (PRI), which ruled Mexico for 70 years until the last election in 2000.
Patricia Mercado is standing for the Social Democrat and Peasant Alternative Party and Roberto Campa is the candidate of the New Alliance.