Bolivia's government has appointed directors to sit on the boards of five foreign energy companies, marking another step in the nationalization of the country's oil and gas sector.

The directors will represent Bolivia's state-owned energy company, Yacimientos Petroliferos Fiscales Bolivianos, which the government says will eventually manage all energy production in the country.

Each of the five companies to be nationalized will have four directors from the state-run oil firm and three representing the foreign owners.

Bolivia's Hydrocarbons Minister Andres Soliz, says the new directors will formally take control once the government completes the acquisition of majority stakes in the five companies.

Last week, Bolivia said the foreign energy companies have six months to renegotiate their contracts or leave the country. Bolivia says the new contracts will require foreign firms to pay higher prices for Bolivian fuel.

Two of the five firms being nationalized are subsidiaries of Brazil's state-owned company, Petrobras. Executives from Petrobras are due to start negotiations with the Bolivian government, Wednesday.

Brazil's foreign minister, Celso Amorim, said Tuesday he expects the negotiations to be long and difficult. Brazil relies on Bolivia for about half the natural gas it consumes.