Activists protesting against the impending construction of the Stung Cheay Areng Hydropower Dam in Koh Kong province have given opposition Cambodia National Rescue Party president Sam Rainsy an ultimatum: show us proof the project will not proceed or we will take to the streets of Phnom Penh.

Rainsy told reporters in October, following a meeting with Prime Minister Hun Sen, that the premier had assured him the controversial project could be “postponed to the next term to let the next generation decide”.

But since the CNRP leader made those comments, the provincial authorities and companies involved in carrying out social and environmental assessments of the potential impacts of the dam have pushed ahead with their plans to finish the feasibility studies.

“Sam Rainsy has to show the written evidence. He has to confirm with Prime Minister Hun Sen again, in writing,” Heng Samnang, an activist with the Khmer Youth Empire, said during a press conference in Phnom Penh yesterday. “The two party leaders said they would not build the dam in this mandate, but [Minister of Mines and Energy] Suy Sem and the Koh Kong provincial authorities did not follow this and they still continue [to move ahead with the project].”

Rainsy’s comments followed a press conference held by Sem, where he said the project would cost $400 million and be finished by 2020.

On Tuesday, two representatives of Sawac Consultants for Development, a firm contracted to carry out the environmental assessment in Areng, tried to reach the isolated valley along with several soldiers, but were blocked by villagers.

This week’s standoff was the latest in a series of escalated actions carried out by activists and local villagers – which began with a road blockade in March – to stop representatives of Chinese state-owned engineering firm Sinohydro Group and its contractors from conducting feasibility studies of the dam’s potential impact.

The dam would displace about 1,300 ethnic Chorng people, according to government figures released in October. The local affiliate of Sinohydro has two of the country’s most influential tycoons on its board of directors, including ruling Cambodian People’s Party Senator Lao Meng Khin.

Ven Vorn, an ethnic Chorng community representative from Koh Kong province, called on the government to order soldiers who have been posted to the valley to leave and for the project to be officially scrapped.

“They deploy soldiers in the area to protect the company and transport logs out illegally and they threaten people,” he said.

Samnang of the Khmer Youth Empire said that the community would wait for four days for Rainsy to respond to their request before beginning street demonstrations “as a last resort”.

“We would like [Rainsy] to answer our questions by Sunday. If there is no resolution, we will commence the demonstrations,” Samnang said.

Nhem Punharith, a CNRP spokesman, declined to comment. Rainsy and other party representatives, who are currently abroad, did not respond to an emailed request for comment by press time.

Ith Praing, a secretary of state at the Ministry of Mines and Energy, declined to comment yesterday, but in a September 30 press conference said the project would proceed if the feasibility studies produced positive results.

Two other Chinese companies – China Southern Power Grid and China Guodian – backed out of the project after completing environmental and social impact assessments.

China Guodian wrote in its annual report for 2013 that it had cancelled the investment because it found the project would not be “economically viable”.

ADDITIONAL REPORTING BY DANIEL PYE