An environmental group says Laos appears determined to build a multi-billion dollar dam on the Mekong River, despite neighboring countries' concerns about the project's economic and environmental impact.

U.S.-based International Rivers says it has obtained a letter sent earlier this month from Laos' energy ministry to the Thailand-based developer of the Xayaburi dam, saying the four-nation Mekong River Commission has completed its decision-making process on the project. No such decision has been publicly announced.

The MRC, made up of Cambodia, Vietnam, Thailand and Laos, asked in April for more information about the project and deferred a decision on whether to approve it until a ministerial-level meeting later this year. Laos announced in May that it would perform an additional study on the impact of the dam.

Vietnam in particular has publicly opposed the project, asking that it be put off for 10 years to permit more study. But the commission's decision is non-binding, meaning Laos can proceed with the $3.5 billion project if it chooses.

Laos is expecting a huge economic boost from selling most of the 1,260-kilowatt dam's hydroelectric power to Thailand. But Vietnam and Cambodia, along with environmental groups, are concerned that the project will disrupt fish migration patterns, affecting the livelihood of millions of people who rely on the river for food.