SANTA CRUZ, Bolivia (CNN) -- Thousands of people in Bolivia's largest state celebrated what they saw as the success of a referendum on autonomy Sunday night, but the country's president said the measure had failed.
Government supporters take part in a demonstration against greater autonomy for Santa Cruz.
Voters in the state of Santa Cruz went to the polls amid sporadic violence Sunday to vote on declaring autonomy from the central government.
Supporters filled the streets of the state's capital city on Sunday night to wave flags and cheer local news reports on exit polls showing that 86 percent of voters approved the referendum.
In a televised address, however, President Evo Morales said the referendum "failed completely."
"This illegal and unconstitutional poll has not had the success that some families and groups in the state of Santa Cruz had hoped for," Morales said.
Official results were not immediately released.
The president said nearly 40 percent of eligible voters did not go to the polls -- and that their absence amounted to a rejection of autonomy effort, which pits an eastern state rich in oil and natural gas with a central government led by a leftist president.
About 20 people were injured in clashes between the two sides Sunday, officials said.
Pro-government peasant groups were blamed for burning dozens of ballot boxes in Santa Cruz, but the state's Provincial Governor Ruben Costas described the violence as isolated incidents.
In addition to the destroyed ballot boxes, pro-government groups blocked roads and attacked polling stations in the districts of San Julian and Yapacani, according to local media reports and video of the incidents.
Costas said he would hold the government of Morales responsible for any acts of violence surrounding the controversial vote. Watch a discussion of the effects of the referendum »
The referendum in Santa Cruz was the first of an anticipated power struggle between the leftist president and three other eastern states. The states are rich in oil and gas reserves and are collectively known as the "media luna" for their half-moon shape.
"It has to be clear that we are not going to accept an interruption of the institutional order by the hand of the Evo Morales' presidency," Costas said.
The matter traces back to July 2006, when 72 percent of voters in the affluent state of Santa Cruz voted for autonomy, as did three of the country's eight other departments -- Pando, Beni and Tarija. All opposed Morales' policies of land reform, energy nationalization, and a new constitution.
The document that spells out the details of the proposal is what voters weighed Sunday.
The crisis has underscored the division between the largely poor Indians, who make up the majority and live in the mountainous western region, and the richer inhabitants -- largely of European descent -- of the eastern lowlands, which are rich in natural gas and minerals.
Morales is Bolivia's first indigenous president.
The governing party had previously not rejected autonomy outright.
"Autonomy as a political model of sub-state organization is viable, is positive and has a high degree of legitimacy," said Cesar Navarro, a leader in the ruling Movement Toward Socialism (MAS) party.
But that's not what Santa Cruz's leaders want to do, he said.
"They are creating a mini-state inside the Bolivian state, and that implies not a state composed of autonomies but a semi-federal state with serious intentions of separatism," he said.
Though Morales has accused the pro-autonomy movement of harboring separatist aspirations, Bolivia's ex-ambassador to the United States, Jaime Aparicio, disagreed.
"It's not a separatist movement," Aparicio told CNN en Espanol. Instead, he said, it is "more of a political response" to Morales' plans to alter the constitution in a way that would grant more power to the nation's indigenous people.
Bolivia's Foreign Minister David Choquehuanca Cespedes called the referendum "nonbinding." He said the proposal "is not compatible with the new constitution or even the constitution that is currently in place."
He said Morales was prepared to negotiate on the issues of concern to the pro-autonomy movement, including discussing new formulas that would result in "more equitable sharing" of taxes and transparent "land management," but the suggestions have not been welcomed by opposition leaders. E-mail to a friend
Journalist Martin Arostegui in Santa Cruz, CNN's Gloria Carrasco in La Paz and David Ariosto in Atlanta contributed to this story.