The United States welcomed Thursday a delay by Southeast Asian nations on approving a controversial hydropower dam in Laos, voicing fear about the environmental effects for the Mekong River.

Laos failed at a meeting to win approval from Cambodia, Thailand and Vietnam to go ahead with the $3.8 billion Xayaburi dam, which activists say could spell disaster for the roughly 60 million people who depend on the waterway.

During a meeting with Mekong nations in July, Secretary of State Hillary Clinton "that there's a very serious question about this new dam and possible environmental ramifications," her spokesman Mark Toner said.

"So we view it as a positive sign that they're delaying looking at it," Toner told reporters in Washington.

The Mekong nations, at their meeting Thursday in Cambodia, called for further study on sustainable development and the potential effects of the project, which would be the first of 11 dams on the mainstream lower Mekong.

Cambodia and Vietnam fear the effects of the 1,260 megawatt Xayaburi dam on their farming and fishing industries. Thailand, however, has been more enthusiastic and has agreed to buy 95 percent of the electricity from the dam.

President Barack Obama's administration launched the Lower Mekong Initiative in hopes of supporting the environment, health and education in the populous region, as part of a renewed effort to build relations with Southeast Asia.