SANTA CRUZ DE LA SIERRA, Bolivia — Soldiers occupied Bolivia's natural gas fields and refineries after President Evo Morales placed his country's vast energy reserves under state control and threatened to evict foreign companies.

The government said soldiers and engineers were sent to 56 locations around the country — including gas fields tapped by foreign companies, such as Britain's BG Group PLC and BP PLC, Brazil's Petroleo Brasileiro SA, or Petrobras; Spanish-Argentine Repsol YPF SA, France's Total SA and Texas-based Exxon Mobil Corp.

The companies have six months to agree to new contracts or leave Bolivia.