Two more forest rangers were suspended Wednesday following the accident in which a truck carrying illegally logged timber overturned fatally in north central Vietnam earlier this month.
Four others were already suspended.
Ten people were killed and five other injured in the accident on December 7 in the province of Nghe An.
A week later four rangers were arrested and suspended, including three escorting the timber on the orders of Trinh Thanh Long, deputy head of the Pu Huong Reserve where the wood was logged.
Pu Huong is part of the Western Nghe An Biosphere Reserve which was recognized by UNESCO as a world biosphere reserve in 2007.
The two suspended now are subordinates of Phan Sy Tuan, chief of one of the six forest ranger stations around Pu Huong and one of the three arrested rangers on the truck.
The Nghe An police have not said who owned the timber.
Pu Huong Reserve has set up a team to inspect the six ranger stations to find out if more officials were involved.
After the incident occurred, Ha Cong Tuan, deputy head of the Vietnam Administration of Forestry, said he was "embarrassed."
He admitted that illegal loggers, forest rangers, and local authorities were colluding in many places to destroy forests.
Figures from his agency show that Vietnam loses nearly 32,000 hectares of forests every year, around 7 percent of it to illegal logging.