1 July 2012 Last updated at 00:10 ETThe main contenders: Lopez Obrador (left), Vazquez Mota (centre) and Pena Nieto (right)
Continue reading the main story



Mexicans are set to got to the polls in a presidential election dominated by the economy and war on drugs.
Ex-governor Enrique Pena Nieto - seen by many as the leading candidate - is attempting to win the presidency back for the PRI party that ruled for years.
His main opponents are left-wing politician Andres Manuel Lopez Obrador, and Josefina Vazquez Mota from the ruling conservative PAN party.
Voters are also choosing a new congress, senate and governors.
Polls are due to open at 1300 GMT across the country. Nearly 80 million voters are eligible to cast their ballots.
Mr Pena Nieto, the 45-year-old former governor of Mexico state, is seeking to bring back the presidency to the PRI (Institutional Revolutionary Party), which held on to power for 71 years until defeat in 2000.
"My priority will be to battle the poverty in our country at its roots," he said during his final campaign rally earlier this week.
But in recent weeks the gap between Mr Pena Nieto and Mr Lopez Obrador, a 58-year-old former Mexico City mayor, has been narrowing, opinion polls say.
Tens of thousands of Mexicans have attended the final rallies
Mr Lopez Obrador, of the Party of the Democratic Revolution (PRD) has also seen his campaign boosted by a student-led movement against the PRI.
The PRD candidate came close to winning the poll six years ago. He accused the governing party of fraud and vote-buying and led a month of street protests against the official result.
But he said things have changed: "In 2006 we lacked organisation, now we are organised. 2012 is not 2006."
The official candidate is 51-year-old Josefina Vazquez Mota, a businesswoman from the ruling National Action Party (PAN).
She has promised to tackle corruption.
With nearly one third of the Mexican population living in extreme poverty, the economy has been one of the main issues in the campaign.
Unemployment remains low at roughly 4.5%, but a huge divide remains between the rich and the poor.
Another issue dominating the campaign is the war on drugs launched nearly six years ago by President Fernando Calderon, who is constitutionally barred from seeking re-election.
The main opposition candidates have been critical of Mr Calderon's policies.
They point out that more than 55,000 people have been killed in drug-related violence since 2006.
Mexicans are also electing 500 congressmen, 128 senators, six state governors, the head of government in the Federal District and local governments.