Tens of thousands of demonstrators marched through Mexico’s capital on Wednesday night to protest a surge in tortilla prices that has put President Felipe Calderon under intense pressure.

Soaring US demand for ethanol has sent corn prices to their highest level in a decade, pulling up prices of Mexico’s national food staple. Protesters held up ears of corn and complained that Calderon, a conservative accused by leftists of stealing the July 2006 presidential election, was failing to protect them against foreign market forces.

“Calderon isn’t just a thief, he’s a murderer because he wants us to die of hunger,” protesters chanted. Calderon’s leftist election rival, Andres Manuel Lopez Obrador, is using the surge in tortilla prices to snipe at the government and he joined the protest march on Wednesday.