Millions of Argentine farmers held nationwide rallies on this week, demonstrating their determination to extend a strike unless the government lowers export taxes on soybeans.

The strike has created a crisis for President Cristina Fernandez, pushing up prices for crucial grains after farmers pledged last Wednesday to hold back shipments to ports for five days and later hold back beef.

"The people are very firm about the strike continuing," said Eduardo Buzzi, President of the Argentine Agrarian Federation during a rally in Armstrong, a central farming hub.

Thousands of farmers demonstrated in cities through Argentina's farm zone, loudly declaring that the government has not met their demands against export taxes linked to global prices.

"We want to negotiate, we want to build a chance for consensus. The government can be on time here to make a reasonable shift in policy," the farm leader said.

Farmers are demanding changes to a sliding-scale export tax system that raised levies on soy and sunseed products.

A study released on Monday showed the public's confidence in the government fell considerably in May from April, hurt in great part by the farm crisis.

"People out here in the country are very indignant," one protester told national television.

Argentina's sliding-scale system links export taxes on grains, oilseeds and byproducts to international prices, raising levies on soybeans to about 40 percent at current prices from the previous fixed rate of 35 percent.

The government last Thursday announced modifications to the taxes. But farm leaders, who want the sliding-scale tax repealed, said the measures did not go far enough.

Corrals at Liniers, Argentina's top livestock market, were empty on Monday, and activities were expected to remain frozen for the day at Rosario, the nation's main grains port.

The conflict has sparked and flared sporadically since the tax came in nearly three months ago, on March 11, and protests have driven up global prices for oils and grains exported by Argentina.

Argentina is the world's No. 2 corn exporter, the third-biggest soy supplier and the No. 4 provider of wheat and beef. (Reporting by Nicolas Misculin, writing by Pav Jordan; Editing by David Gregorio)