Hanoi - The Vietnamese government Thursday announced the results of its investigation into the collapse of a 343-million-dollar bridge last September that killed 54 construction workers and injured 80 others.

The probe concluded an imbalance in the foundation of a temporary buttress was the main cause of the collapse of a section of the 2.7-kilometer Can Tho Bridge spanning Hau River in Vietnam's southern Mekong Delta.

"The imbalanced subsidence of one of the buttresses, the main cause leading to the collapse of the bridge, was as an unforeseen circumstance in regular design," the government said.

The 74-meter section of the bridge collapsed on September 26 when more than 200 workers were working at the site, sending tons of concrete tumbling about 30 meters onto the banks of the Hau River.

The accident killed 54 workers and injured 80 others. The last body was removed from the site on October 17.

Construction on the Can Tho Bridge, touted as South-East Asia's longest cable bridge, began in 2004 with Japanese funding. It was slated for completion in 2008.

The four-lane bridge was designed to offer an alternative to river ferries that now carry about 87,000 passengers and 20,000 cars daily across the Hau River, a tributary of the Mekong, between Can Tho and Vinh Long provinces.

So far, no one has been arrested for the collapse of the bridge, but a government official said the main contractor, Taisei-Kajima-Nippon Steel of Japan, and the subcontractors, Nippon Koei and Chodai, had "compensated the victims and their families with the highest responsibility."

"The Ministry of Public Security has launched a criminal investigation into the case, based on the result of the investigation into the cause of the collapse," Minister of Construction Nguyen Hong Quan was quoted as saying. (dpa)