The US on Friday urged Mekong nations to learn from its mistakes in river infrastructure projects, as Laos confirmed it has postponed a controversial multi-billion dollar dam project.

The $3.8 billion hydroelectric project at Xayaburi has sharply divided the four Mekong nations -- Laos, Vietnam, Cambodia and Thailand -- who rely on the river system for fish and irrigation.

US Secretary of State Hillary Clinton pressed for further environmental assessments before proceeding with the project during a meeting with Mekong countries in the Cambodian capital, echoing calls from Hanoi and Phnom Penh who worry the dam could decimate their fishing and farming industries.

Clinton, who called the Mekong river basin "a miracle", said Washington would help fund studies on the impact of proposed dams on the river, on which some 60 million people depend for transportation, food and economy.

"I'll be very honest with you. We made a lot of mistakes," Clinton said in her opening remarks, offering the assistance of her country's Mississippi river commission to the Mekong nations.

"We've learned some hard lessons about what happens when you make certain infrastructure decisions and I think that we all can contribute to helping the nations of the Mekong region avoid the mistakes that we and others made," she said.

The Mississippi, one of the longest rivers in the US, has struggled with a number of river projects over the years that have led to floods, water flow issues and sediment problems.

Laos Foreign Minister Thongloun Sisoulith said after the talks in Phnom Penh that he had assured his Mekong counterparts the Xayaburi dam was on hold until its neighbours' environmental concerns were answered.

"The Laos government decided to postpone, we have to study more," he told reporters.

Environmentalists fear the proposed 1,260 megawatt dam, the first of 11 on the key waterway, will have disastrous environmental effects and harm the livelihoods of millions of people.

Communist Laos, one the world's most under-developed nations, hopes the dam will help it become "the battery of Southeast Asia" and plans to sell most of the electricity to Thailand.

But there is opposition to the project in Thailand too, and Thai Mekong river basin villagers said through a lawyer on Friday they would seek a court ruling to ban Thailand's state electricity giant from buying power from the dam.