While the commission's decision had been widely anticipated following Tuesday's meeting of representatives from Cambodia, Laos, Thailand and Vietnam, the group instead deferred the final decision on the construction of the Xayaburi dam to the ministerial level. No date was set for a final decision.
The Mekong Agreement stipulates that all four countries must approve major projects on the lower Mekong River.
The Xayaburi dam is the first of 11 hydropower dams -- nine in Laos and two in Cambodia -- proposed along the river. About 95 percent of the project's 1,260 megawatt capacity is intended for export to Thailand.
Environmentalists have maintained that the proposed Xayaburi dam poses a threat to the environment and surrounding communities.
International Rivers says the project would forcibly resettle more than 2,100 people and directly affect more than 202,000 people. Also, 41 fish species could be threatened with extinction and an additional 23 to 100 migratory fish species would face a blocked migration route, thus affecting the livelihood and food security of millions of people in the region, the group says.
"Today the Mekong River has gotten a much-needed but temporary reprieve," said Ame Trandem, Mekong campaigner with International Rivers, in a statement Tuesday. "The Mekong River is a valuable shared resource and the Xayaburi dam's transboundary impacts require agreement between the region's governments and the public."
The WWF has called for a 10-year delay in the approval of the Xayaburi and other mainstream dams. Immediate energy needs, WWF says, instead can be met from multiple hydropower projects on selected Mekong tributaries where connectivity affects would be lower.
U.S. Sen. Jim Webb, D-Va., chairman of the Senate Committee on Foreign Relations Subcommittee on East Asian and Pacific Affairs, last week called for a delay in construction of any mainstream dam along the Mekong until adequate planning and multilateral coordination could be guaranteed.
"Numerous scientific studies have concluded that construction of the Xayaburi dam and other proposed mainstream dams will have devastating environmental, economic, and social consequences for the entire Mekong sub-region," said Webb in a statement.
The Bangkok Post reported Sunday that roadwork had begun near the proposed site. Some villagers were preparing to be resettled from the area, for compensation as little as $15, the Post said.