Colombian President Álvaro Uribe's plan to manually eradicate 250,000 acres of coca plants this year ran into violent opposition last week as some 2,000 peasants blocked a highway outside Medellin, smashed a toll booth, and fought with police in protest of Uribe's campaign. The peasant farmers are demanding two years to shift to legal crops.

A few days later, the violence over coca cultivation spread to the Venezuelan border, where two soldiers and three leftist rebels were killed in clashes over coca fields. The soldiers and rebels died in a Monday clash in Santander province.

The US and Colombian governments have spent billions of dollars in recent years in efforts to eradicate coca crops there, but the country remains the world's leading coca and cocaine producer. The protests by peasants and shoot-outs between soldiers and rebels illustrate the obstacles faced by Uribe and his allies in Washington.

For the peasant farmers outside Medellin, protecting their coca crops is a matter of survival, said local officials. "They are asking for solutions to their food security and sustenance," the mayor of the town of Tarazá, Miguel Ángel Gómez, told Reuters.

"We're protesting because if they finish off the illegal crops, which we all know are illegal and damaging, then they finish off our way of sustaining our families," one farmer told local television.

The Colombian government has blamed the Revolutionary Armed Forces of Colombia (FARC), the country's largest guerrilla group, with fomenting the protests. Like many other actors in the Colombian conflict, the FARC profits from the coca and cocaine trade.