Energy-starved Laos sought the green light from Southeast Asian neighbours on Thursday for a proposed hydropower dam on the Mekong River that faces fierce opposition from conservationists.

The landlocked nation held high-level talks with Cambodia, Thailand and Vietnam -- the three other members of the Mekong River Commission -- in the Cambodian city of Siem Reap to discuss the $3.8 billion Xayaburi project.

Activists warn that the vast 1,260 megawatt dam in Laos, the first of 11 planned for the mainstream lower Mekong, could spell disaster for the roughly 60 million people who depend on the waterway.

Thailand, which has agreed to purchase some 95 percent of the electricity generated by the dam, had already indicated that it would not oppose the project at Thursday's meeting of environment ministers.

But Vietnam and Cambodia, wary of the dam's impact on their farm and fishing industries, have expressed strong concern and are calling for more studies to be carried out before it is allowed to go ahead.

Vietnam has even proposed a 10-year moratorium on all hydro-electric projects on the lower Mekong.

Despite such worries, any decision made at Thursday's meeting will not be legally binding on Laos.

The tiny country is one of the poorest in the world and sees hydropower as vital to its potential future as the "battery of Southeast Asia", selling electricity to its more industrialised neighbours Vietnam and Thailand.

In response to criticism of the project, Laos in May said it had suspended work on Xayaburi and commissioned a new review.

Last week, Laos indicated it should be allowed to go ahead, as "this dam will not impact countries in the lower Mekong River basin", deputy minister of energy and mines Viraphon Viravong told the official Vientiane Times.

Cambodia said this was not enough and called for further examination of cross-border impacts of the multi-billion-dollar project before a final decision is made.

Environmentalists have warned that damming the main stream of the river would trap vital nutrients, increase algae growth and prevent dozens of species of migratory fish swimming upstream to spawning grounds.