By Charles Scanlon
Mr Morales has taken over several companies since taking power in 2005
Bolivia's government has seized control of a foreign-owned energy company two days before the country votes on a proposed new constitution.
President Evo Morales flew to a natural gas field in central Bolivia to order the immediate nationalisation of Chaco energy company.
He said the country was taking back control of its natural resources "little by little".
Troops earlier occupied all the company's offices and installations.
Chaco, which was a subsidiary of the British oil company, BP, had been in talks with the government about the transfer of shares, but negotiations broke down.
Opposition politicians described the move as a political manoeuvre, coming just two days before a hotly contested referendum on a new constitution that would consolidate state control over the economy.
President Morales has already nationalised most of the energy industry and has promised to take over other sectors of the economy as well.
Speaking inside the Chaco offices, Mr Morales said his government "will respect private investment as long as they respect Bolivian norms."
"We want partners, not bosses," he added.
The new constitution would entrench state control of the economy and give more power to Bolivia's poor indigenous communities.