Housewives vented their frustrations and anger at Felipe Calderon when he appeared in public this week and pleaded him to bring down tortilla prices that have risen by as much as 400 per cent in recent months.

Millions of Mexicans eat a daily dose of tacos - tortillas wrapped around food like beans and chicken. According to Government estimates about half of the country's 107 million population live in poverty and for those families tortillas are the main source of calories.

Their price has risen steeply across Mexico and has reached 30 pesos ($2.72) a kilogram in Durango state, according to La Jornada newspaper - up 400 per cent from 6 pesos (54 cents) in November. The price hike has become unbearable for many families who have to survive on the country's minimum wage of about $4.50 a day.

"When there isn't enough money to buy meat, you do without," said Bonifacia Ysidro. "Tortillas," she added, "you can't do without."

Mrs Ysidro said she paid 25 pesos - about a sixth of her household's combined daily income - for enough tortillas to feed her family of six.

"If I don't have that much, I'll have to buy less," she said. "If it goes higher, what am I going to give my children?"

Leticia Balino, who runs a tortilla shop behind the American Embassy in Mexico City, said many of her customers are complaining, especially those with large families. "They say, 'How is it possible that the price could rise so much in such a short time?"' she said.

Mexico now imports much of its corn from the United States, where prices have rocketed 80 per cent to their highest levels in a decade last year due to demand for corn-based ethanol fuel. Government officials say, however, that the leap in tortilla prices has as much to do with speculation and hoarding by traders as it does with the high US prices.

In response to demand to intervene, Mr Calderon said: "We will take all the measures within reach of the federal government to avoid escalating prices." But he added that the Government did not fix tortilla prices.

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

The Federal Competition Commission regulatory body said it will launch a probe 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.

Mr Calderon vowed to clamp down on price speculators, hold down the price of some corn flour sold by the government and scour the planet 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.

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