MEXICO CITY, (Reuters) -- Mexico ramped up security at its international airport, power plants and oil refineries on Friday, as leftists challenging a tight presidential election result threatened to intensify crippling protests. Supporters of leftist Andres Manuel Lopez Obrador, who claim his narrow defeat in the July 2 election was rigged, warned they would step up civil disobedience unless the country's electoral court orders a full vote-by-vote recount.
"Security has been reinforced, as a preventive measure, to safeguard the operations of installations," Energy Minister Fernando Canales told reporters.
With the center of Mexico City already paralyzed by protesters, the government took precautions against attempts to block the city's airport.
Dozens of police in riot gear patrolled the airport and approach roads. Some briefly detained a Reuters photographer whom they thought was a leftist scouting out the area to organize a protest.
"Security has been stepped up," government spokesman Ruben Aguilar said. "Mexico City airport will always be in operation."
Mexico City's recently enlarged Benito Juarez airport is one of the busiest in Latin America, with hundreds of daily international and domestic flights that are crucial to the country's multibillion-dollar tourism industry.
Extra safeguards were also put in place at power plants, refineries and other oil industry facilities.
The state-owned oil industry is another key economic pillar, generating one-third of government revenues, and a symbol of national sovereignty.
Lopez Obrador is from the oil-rich state of Tabasco and staged marches there and blockades of oil wells to protest a governor's race he lost in 1994.
Also, some 100 protesters on the Mexican side of the border partially blocked a road bridge uniting the United States and Mexico across the Rio Grande.
