Demonstrators say the electoral law changes approved last week threaten democracy and could mark a return to past practices of vote manipulation.

The president posted an image on Twitter of what he claimed was an "aluxe," a small, mischief-making, woodland spirit from Mayan tradition.

The outbreak of violence occurred during a testing week for the government of President Andres Manuel Lopez Obrador, who on Friday said he would not accept any foreign intervention in Mexico to deal with violent criminal gangs.