VIENTIANE, July 30 (Xinhua) -- The Lao government will work with countries whose companies are stakeholders in the Xe-Pian Xe-Namnoy hydropower project to investigate the cause of the collapse of the project's saddle dam, Prime Minister Thongloun Sisoulith said on Sunday.

The 410 MW capacity hydro plant is a joint venture between SK Engineering and Construction (South Korea), Korea Western Power (South Korea), Ratchaburi Electricity Generating Holding PCL (Thailand), and Lao Holding State Enterprise (Laos).

The hydropower reservoir's saddle dam D collapsed on July 23, causing flash floods swamping villages in Sanamxay district of Attapeu province, some 560 km southeast of Lao capital Vientiane, leaving at least nine people dead as of Sunday and with more than 100 still declared missing.

Thongloun pledged a thorough investigation into the cause of the collapse, saying it would take place in a transparent and just manner, local online newspaper Vientiane Times reported on Sunday.

"The government of the Lao People's Democratic Republic will cooperate with the governments of countries whose companies have been registered (as a stakeholder) to address this issue," he said while visiting the Ministry of Labor and Social Welfare to check the donation of relief supplies.

"The government will also look into the responsibilities of the authorities," he added.

Thongloun pledged that the government, with support and assistance from all sectors, friendly countries and international organizations, would do its utmost to search for and rescue all the missing and to provide relief assistance and rebuilding local communities.