At least two people have been killed and more than 70 injured in clashes in the Bolivian city of Cochabamba.
Protesters battled each other and police with guns, sticks and rocks
The violence involved thousands of rival protesters at odds over a regional governor's call for a referendum on greater local autonomy.
Supporters of President Evo Morales say Manfred Reyes Villa is trying to undermine Mr Morales's authority.
Tension is increasing between Mr Morales and several elected governors who want more autonomy.
'A political tool'
The protests began four days ago when supporters of the president, the majority of them coca growers, converged on Cochabamba's streets, calling for the resignation of Mr Reyes Villa.
Police dressed in riot gear used tear gas to disperse rival protesters, who battled each other with guns, sticks and rocks.
Many accuse Mr Reyes Villa of working to undermine the authority of President Morales - himself a former coca-grower and the nation's first indigenous president.
The Cochabamba governor - who was elected with 48% of the vote in 2005 - maintains that he has no reason to resign and has every intention of pressing ahead with his plans for the referendum, regardless of the violence.
Mr Reyes Villa is backed by five other governors, most from the country's wealthiest eastern provinces, who are also seeking greater autonomy.
They oppose some of the plans of President Morales who has nationalised the country's energy sector and now hopes to have a new constitution approved and implement land reform.