Supporters of leftist candidate Andres Manuel Lopez Obrador targeted federal offices in escalating protests over allegations of electoral fraud, as officials started a partial recount of votes from last month's disputed presidential election.
On Tuesday, hundreds of activists blockaded the entrance to the Agriculture Department and forced open highway toll booths for cars to stream through free-of-charge during rush hour -- the latest in a wave of protests to demand a total recount of the presidential election.
Lopez Obrador was the runner-up in an official count that gave ruling party candidate Felipe Calderon an advantage of 0.6 percent, or about 240,000 votes.
The protests will continue all week, Lopez Obrador said, culminating in what he called an "extraordinary rally" in Mexico City on Sunday, the day officials are expected to finish recounting votes in about 9 percent of the nation's polling places.
"We are going to carry on our struggle ... We are sure we will triumph," the silvery haired leftist told tens of thousands of supporters in the capital's central plaza on Tuesday night.
Lopez Obrador, the former mayor of Mexico City, is demanding that officials count all 41 million ballots, but a tribunal said that they will only review votes in places where there is evidence the ballots could have been miscounted. The partial recount started yesterday.
While Lopez Obrador has urged his followers to remain peaceful, tensions are growing and some fear that he may not be able to prevent the demonstrations from erupting in violence.
The seizure of the toll booths, which gave more than 7,000 motorists a free passage to the capital, prompted President Vicente Fox's spokesman, Ruben Aguilar, to threaten for the first time the use of force. But demonstrators backed off before that could happen, abandoning the booths shortly after the end of morning rush hour.
Fox criticized the protests saying, "Democracy cannot advance without respect for others and above all without respect for institutions."
Late on Tuesday, the federal attorney general's office opened up a criminal investigation into the seizures, according to Mexican media. Officials at the agency could not immediately be reached.
An official in Lopez Obrador's leftist Democratic Revolution Party said the occupying of toll booths was the start of a new type of protest that would take place across the nation.
"Until now we have concentrated an important part of our protests in the capital, but in this new stage we are going to carry out actions all over the country," party secretary-general Guadalupe Acosta said. "They will be coordinated, national actions with the same objective: that they open the boxes and count the votes."
The Agriculture Department in Mexico City was bockaded on Tuesday by demonstrations for more than six hours.
Lopez Obrador supporters who gathered in front of the nation's top electoral court on Monday night raised their fists in defiance.