Mexico City (CNN) -- Hours after Mexico's presumed president-elect, Enrique Peña Nieto, said it was time for his country to leave behind the political rancor of campaign season, his closest opponent in the polls refused to concede and said the vote had been "plagued by irregularities." 

Andres Manuel Lopez Obrador, who election authorities projected as the runner-up in Sunday's presidential vote, said Monday that he was awaiting the official election results, and prepared to contest them before judicial authorities if they didn't turn out in his favor. 

"The election was plagued by irregularities before, during and after the process," said Lopez Obrador. 

The Democratic Revolution Party candidate's declarations echoed comments he made in 2006, when election authorities said the leftist candidate narrowly lost the presidential race to Felipe Calderon. Lopez Obrador claimed election fraud and never conceded, referring to himself afterward as "the legitimate president of Mexico." 

His supporters protested nationwide. In Mexico City, they staged sit-ins and blockades. 

On Monday, Lopez Obrador called on his supporters to wait for the official results. The Federal Election Institute's verification of individual poll results begins Wednesday. 

Earlier, Peña Nieto, who election authorities projected as the winner of Sunday's presidential vote, told CNN en Español he was ready to work across party lines to build a better Mexico. 

"We have to be constructive and put aside our differences, which are only for competitions and electoral contests," Peña Nieto said Monday. "Yesterday I indicated that (after) this tense and divisive atmosphere, which is natural in all democratic contests, we have to turn the page and move on to enter another chapter, another moment in our political lives, with a willingness and spirit that are constructive and purposeful." 
Who is Manuel Lopez Obrador?
Does he think something was wrong with the election?
What office was he running for?
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Did he ever run for that office before?
When?
Who won then?
Who won this time?
What did Obrador's supporters do?
Which agency is verifying the election results?
Which US news agency did the winner talk to?
What name did Obrador give himself after the 2006 election?
Has he conceded this election?
the runner-up in Sunday's vote
the runner-up in Sunday's presidential vote
he claimed election fraud
Lopez Obrador claimed election fraud
president
the presidential race
Mexico
after Mexico's presumed president-elect,
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 candidate's declarations echoed comments he made in 2006
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comments he made in 2006
to Felipe Calderon
to Felipe Calderon
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Peña Nieto, who election authorities projected as the winner 
His supporters protested
His supporters protested
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CNN
Earlier, Peña Nieto, who election authorities projected as the winner of Sunday's presidential vote, told CNN 
the legitimate president of Mexico
the legitimate president of Mexico
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his closest opponent in the polls refused to concede