Lim Kean Hor, Cambodia's water resources minister and its representative to the Mekong River Commission (MRC), an intergovernmental body of four countries that share the river, demanded in a letter to his Lao counterpart Noulinh Sinbandhit that construction on the dam be suspended pending an environmental impact assessment.
"Cambodia's position is that Laos should halt the dam construction while the environmental impact study is being carried out," the Cambodian minister said in the statement, according to Cambodian online newspaper CEN
The letter comes weeks after Sin Niny, vice-chairman of Cambodia's Mekong Committee, threatened that Cambodia could file a complaint against Laos in an international court if it allowed the dam - which would be the first mainstream dam on the Lower Mekong -to be built without regional consensus.
Since the December agreement to suspend construction, the Thai company Ch Karnchang announced it has signed contracts for the construction of the dam beginning March 15.
Through the MRC, established in 1995, Cambodia, Laos, Thailand, and Vietnam have agreed to a protocol for consulting with and notifying each other about use of Mekong resources, but the organization has no binding jurisdiction.
Meanwhile in Thailand, which will buy nearly all the power generated by the hydro-electric project, opposition to the dam has escalated, with representatives from the country's riparian provinces holding a demonstration outside a MRC conference in Phuket last week.
About 30 protesters representing members of riparian communities in Thailand's eight provinces along the Mekong gathered outside the MRC's Mekong2Rio conference, an international gathering of on transboundary water resources management.
The group's protest followed larger demonstrations outside the Bangkok headquarters of Ch Karnchang and Thai banks providing loans to finance the project.
The protesters are concerned that the dam, which would block fish migration on Southeast Asia's main waterway, could impact the lives of millions in the region who rely on the river for their food and their livelihoods and pave the way for other hydropower projects on the river.
At least 11 other dams have been proposed on the mainstream Lower Mekong, in addition to five already built on the upper part of the river in China.
The protesters were allowed a brief meeting with the MRC chief executive officer Hans Guttman, who told them only preliminary construction had begun around the Xayaburi site and that the commission would consider the concerns of local people, according to Thailand's The Nation newspaper.
The day before the protests, representatives from more than 130 civil society groups issued a statement backing a report that proposes an alternative power plan for Thailand that excludes the Xayaburi dam.
The report, produced by Thai energy experts Chuenchom Sangasri Greacen and Chris Greacen, was presented to the country's Energy Regulatory Commission on Friday and recommends Thailand seek sources of energy with environmental impact less damaging than that of the Xayaburi dam.
The report, "Power Development Plan (PDP) 2012 and a Framework for Improving Accountability and Performance of Power Sector Planning", criticizes the country's plan for investing in energy infrastructure and recommends ways where energy use could be reduced.
"If we can invest in the know-how to manage energy consumption, in sustainable energy, and in production efficiency, not only will the price of electricity be lower, but we can also avoid ... importing energy from high-impact dams such as Xayaburi," Chuenchom Sangasri Greacen told RFA.
She said that Thailand's energy planning process is flawed and that the country should invest in efficiency measures and alternative energy instead.
"We have a better alternative," she said. "According to energy conservation policy, we should invest more in the area of producing better electrical devices, or the standard of buildings instead of building new power plant, or building hydroelectric dams that create impacts to environment."
Radio Free Asia