(CNN) -- At least 16 people have been killed in fighting between Bolivian government forces and supporters of an autonomy movement in the east of the country, according to the nation's interior ministry.
The fighting is centered in the eastern province, or department, of Pando, where the government declared martial law on Friday.
The order came as a C-130 plane carrying federal troops landed in the town of Cobija in Pando, at a civilian airport that had been controlled for the past week by pro-autonomy forces.
The rift within Bolivia centers around the four eastern departments of Santa Cruz, Pando, Beni and Tarija, where natural gas deposits have made them richer than the rest of the nation.
President Evo Morales, the nation's first Indian president, has promised to redistribute wealth from the eastern departments to the highlands, which sparked the autonomy movement.
Morales has accused the United States of fomenting the unrest, an assertion the U.S. State Department has rejected as "baseless."
Some of Latin America's leaders have supported Morales, with Venezuelan President Hugo Chavez expelling U.S. Ambassador Philip Goldberg from Caracas in solidarity with Bolivia and recalling his own from Washington. Bolivia also expelled U.S. ambassadors.
There were varying reports about the number of deaths from the fighting. Some local officials were saying Saturday that more than 20 had been killed.