The leaders said Mr Morales' mandate had been ratified by a big majority
An emergency summit of South American leaders to discuss the turmoil in Bolivia has given its full backing to President Evo Morales.
Nine presidents condemned last week's political violence in which 30 people were killed, and called on Bolivia's opposition to end its protests.
The opposition is angry at government plans for a new constitution.
Mr Morales has likened the unrest in opposition-controlled regions of his country to an attempted coup.
He said the emergency meeting of the Union of South American Nations (Unasur) in Santiago, Chile, was important as democracy had to be defended not only in Bolivia but all of South America.
The unrest, in which protesters have blocked roads and occupied public buildings, represents the most serious challenge to Mr Morales since he took office almost three years ago.
In a statement, the regional leaders offered "their full and firm support for the constitutional government of President Evo Morales, whose mandate was ratified by a big majority".
They warned that any government formed following an illegal removal of Mr Morales would not be recognised as legitimate.
Arriving in Santiago for the meeting, Mr Morales said he had come "to explain to the presidents of South America the civic coup d'etat by governors in some Bolivian states in recent days".
The unrest centres on his decision to hold a referendum on a new constitution in December.
Mr Morales says he wants to re-distribute Bolivia's wealth and give a greater voice to the country's large indigenous community.
But opposition leaders oppose the plan and have demanded greater autonomy as well as more control over natural gas revenues in their areas.
Trouble has flared in several eastern provinces and cities last week. Mr Morales declared martial law in the Pando region on Friday.
Downturn in relations
Daniel Schweimler, the BBC's correspondent in the region, says that no one in South America wants the situation in Bolivia to escalate.
Mr Morales wants to give more rights to Bolivia's indigenous community
Neighbouring Brazil and Argentina are particularly worried about their supplies of natural gas, which come from the east of the country where the dispute is at its most severe.
But, our correspondent adds, it is not clear what the meeting in Chile can achieve. Representatives of Bolivia's opposition did not attend the summit.
There have been some talks between the two sides, however.
On Sunday night Bolivian Vice-President Alvaro Garcia met opposition representative Mario Cossio, the governor of Tarija province. They agreed to hold more talks when Mr Morales returns from Chile.
The unrest in Bolivia has triggered a downturn in relations with the US.
Last week Bolivia accused the US of supporting the opposition and expelled its ambassador. Venezuela followed suit to show solidarity and Honduras has refused to accept the credentials of a new US envoy.
Venezuelan President Hugo Chavez said the unrest in Bolivia was "a conspiracy directed by the US empire", likening it to the 1973 CIA-backed coup which ousted Chile's President Salvador Allende.
The US says it regrets the recent diplomatic expulsions and has rejected Bolivia's allegations against its ambassador.