Ecuador on Thursday licensed a state company to develop oil reserves in Yasuni, a huge nature preserve in the Amazon rain forest.
The license comes just days after a petition for a referendum on the project was rejected by the country's election authorities.
The action, signed by Environment Minister Lorena Tapia, gives a state company, Petroamazonas, rights to develop an oil field in part of the forest designated a UNESCO Biosphere Reserve.
Home to two indigenous tribes that have resisted contact with the outside world, the rainforest park covers an expanse of more than 9,800 square kilometers (6,090 miles) between two rivers.
The field, known as Tiputini, is part of a vast bloc that lies partially within the park with proven reserves of 920 million barrels of crude.
Petroamazonas was also granted a license to develop the Tambococha field, which lies outside the park but within the same oil development bloc.
Yasunimos, an environmentalist group, has fought government plans to open the park to oil development, gathering what it said were nearly 728,000 signatures on a petition to put it to a referendum.
But on May 9, Ecuador's National Electoral Council invalidated half the signatures and rejected the petition, clearing the way for Thursday's action.
The decision, however, could be appealed to the country's constitutional court.
In October, Ecuador's Congress approved a government plan to develop the Yasuni oil reserves, on the promise that revenues would be used to eradicate poverty.
Explore further: Ecuador's Yasuni dilemma: a reserve full of life, and oil