President Lopez Obrador has cast past administrations as deeply corrupt and made combating graft his top priority. At least 40 percent of registered Mexican voters, or some 37 million people, would need to vote for the results to be binding.
All 500 seats in the lower house, 15 state governorships and thousands of local leadership positions are up for grabs, with some 93.5 million Mexicans eligible to vote.
At least 24 people died and dozens others were injured on Monday night in the accident, one of the worst ever to strike the Mexico City metro, raising questions about construction and maintenance standards on a network used by millions every day.
The official apology came amid broader commemorations of the 500th anniversary of the 1519-1521 Spanish Conquest of Mexico, and 200 years of Mexico’s 1821 independence from Spain.
Near the front of the colonial-era building that serves as the president's offices, activists wrote: "Victims of Femicide" in huge letters across the top of the barriers, with the names under.
US-Mexico border is a major crossing point for migrants fleeing poverty, drug-related violence and other woes in Mexico and Central America.
Responding authorities seized 18 long firearms, one short, two vehicles and two grenades at the site of the clash.
The clashes between hundreds of US-bound Central Americans and the Mexican National Guard underscores the challenge President Andres Manuel Lopez Obrador faces to contain migration at the bidding of his US counterpart Donald Trump.
Mexico's foreign minister has gradually announced more commitments to beef up border infrastructure in an effort to stave off a threat of tariffs by US President Donald Trump.
Mexico's President Andres Manuel Lopez Obrador says his country is "doing our job" to stop the flow of undocumented migrants to US, warns Trump that imposing tariffs would be a lose-lose game.
Mexicans forced from their villages by violent drug gangs are seeking assurances from the president for their security if they go home. But a safe return may still be a while away.
Veteran leftist Andres Manuel Lopez Obrador who will be sworn in as Mexico's next president on Saturday vowed to champion the poor and contain business elites.
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