Tortillas are part of the daily diet for millions of Mexicans in the form of tacos, and wraps for a variety of foods such as beans and chicken.

For many poor families, tortillas are the main source of calories but prices have climbed steeply across Mexico in recent weeks. The La Jornada newspaper reported prices reaching 30 pesos ($2.72) a kilogramme in Durango state, representing a 400 per cent increase from 6 pesos (54 cents) in November.

The minimum wage in Mexico is about $4.50 a day and, according to the government, about half of the country's 107 million citizens live in poverty.

"I don't care if they have to bring it from thousands of kilometres"

Felipe Calderon
Angry housewives have shouted at Calderon at public appearances this week and Andres Manuel Lopez Obrador, who narrowly lost last July's presidential election to Calderon said "The tortilla has never cost so much in the country's history."

Mexico, considered by many archeologists as the birthplace of corn, now imports much of the grain from the United States, where prices rocketed 80 per cent to their highest levels in a decade last year because of demand for corn-based ethanol fuel.

One of Calderon's main priorities since taking office in December has been to try to convince poor Mexicans he has their interests at heart.

Federal investigation

He promised to clamp down on price speculators, hold down the price of some corn flour sold by the government and look elsewhere for cheaper grain to import.

"I don't care if they have to bring it from thousands of kilometres, what matters is that this is not an argument to raise prices," he said while on a tour in the state of Veracruz.

But he could come into conflict with some of his key supporters in big business after the Federal Competition Commission regulatory body said it will launch an investigation into tortilla prices.

"The objective of the investigation is to determine whether there is any collusion to fix prices, restrict amounts of the goods or divide markets between competitors," it said.

Mexico lifted price controls on tortillas in the 1990s, and is unable to directly fix the cost of the foodstuff.

Mexican consumers also are coping with higher prices for other staples. The cost of white bread and fresh fruit and vegetables all rose more than inflation in 2006, according to the central bank.

The tortilla increase outpaced inflation and minimum wage hikes of about 4 percent for the past year.