Militant Colombian rebels are infiltrating an increasingly violent national strike by farmers and state workers, the country's defence minister says.

Juan Carlos Pinzon on Thursday blamed the Revolutionary Armed Forces of Colombia (FARC) for mobilizing groups of demonstrators who threw rocks and explosives at police on the 11th day of protests against President Juan Manuel Santos's agricultural and economic policies.

"Everyone knows that the terrorist FARC end up infiltrating these kinds of protests and cause disorder," Pinzon told reporters in the capital of Bogota.

"There are sectors that infiltrate these situations because, let's be frank, potato farmers, valuable people, workers, are not really prepared to use explosives against the police or burn cars; there has to be evil minds behind that."

Demonstrators have clashed with police after blockading roads, snarling traffic into cities. At least one protester was killed and scores injured after police began dismantling the barricades on Aug. 19.

The Marxist rebel group FARC, listed as a terrorist organization by the Canadian government, issued a statement in support of the demonstrations Monday.

The group is in peace negotiations with the Santos government, seeking to end the deadly insurgency that has gripped the country since 1964.

With files from Reuters