LA PAZ, Bolivia (CNN) -- Heads of South American nations lent support Monday night to President Evo Morales of Bolivia, who says opposition leaders are trying to overthrow his government.
Indigenous people from El Alto, Bolivia, take part in an anti-U.S. demonstration in La Paz on Monday.
Confronting their first crisis, members of the four-month-old Union of South American Countries voted to create a commission to support Morales' democratically elected government, said President Michelle Bachelet of Chile.
She read a nine-point statement on Chilean TV that calls for the support of human rights and democracy and the preservation of Bolivia's territorial integrity. The statement condemns any attempts to overthrow the government.
It also said the new commission would investigate a reported massacre in the Bolivian state of Pando, where violent clashes killed 30 people last week. Those clashes pitted supporters of eastern governors who want autonomy against the central government.
The South American leaders also urged dialogue to address disputes in Bolivia.
Morales attended the emergency meeting of the union, which is modeled on the European Union and aims to politically and economically integrate South American countries.
The president is poised to approve the start of negotiations between his leftist government and opposition leaders of five provinces who demand greater autonomy and the cancellation of a constitutional referendum that would give the president more power. The opposition also is angry over tax money that Morales is diverting from the provinces to fund elderly programs.
Morales said the opposition leaders are trying to overthrow the government.
"This is a coup in the past few days by the leaders of some provinces, with the takeover of some institutions, the sacking and robbery of some government institutions and attempts to assault the national police and the armed forces," Morales said.
Opposition leaders say they merely want their demands met.
Police kept order Monday during a march by about 2,000 pro-government groups opposed to the violence in the provinces. The demonstrators marched past the U.S. Embassy in La Paz.
Morales expelled the U.S. ambassador to Bolivia last week, blaming the American government for inciting the violence. The United States called the accusations "false and baseless" and said Bolivia was making a "grave mistake."
Most of South America's leaders attended Monday's emergency summit, with the exception of President Alan Garcia of Peru. Protest leaders asked to attend the summit in Santiago, Chile, but it was limited to heads of state.
The protests started 21 days ago in Pando, Beni, Santa Cruz, Tarija and Chuquisaca provinces. The opposition groups have blockaded major roads and threaten to disrupt the nation's natural gas shipments, particularly to Brazil and Argentina.
Anti-government protesters also have clashed with police and taken over offices and buildings in the five provinces. Watch some of the violent demonstrations across Bolivia »
Much of the violence has taken place in Pando -- Morales declared martial law there Friday.
On Monday, supporters of Morales, or his so-called militias, were gathering in Santa Cruz, and threatening to encircle the city, stoking fears that blood could be shed there. In Pando, it was reported that arbitrary arrests were taking place as the military took to the streets. Houses had been broken into and shot up, and civic leaders were fleeing to Brazil.
It was uncertain, meanwhile, whether the Bolivian military remained solely behind Morales. Some signs of divisions had been seen within the military.
Opposition leaders say they will not negotiate if there are any more deaths. Vice President Alvaro Garcia said the government will not negotiate about the dead citizens but will rigorously pursue those responsible for the killings.
There are conflicting reports over who killed the 30 peasants. Opposition leaders say the peasants were ambushed by local forces. The government says the peasants were armed and initiated the firefight.
The opposition has offered to lift the blockades as a goodwill gesture, but the government demanded that the protesters also relinquish the buildings and other property they have seized.
Morales, Bolivia's first indigenous president, was elected in December 2005.
CNN's Ione Molinares and Journalist Martin Arostegui contributed to this report.