The official, from the Construction Ministry, told Reuters approval should be a formality. "Now that the committee has passed the plan, there should be no problems," she said. "I think the prime minister will approve it soon."

Environmental groups have said the plan to run the highway through the Cuc Phuong park, which starts about 90 km (56 miles) south of Hanoi and was inaugurated by late independence hero Ho Chi Minh, poses a serious threat to endangered species.

They say Cuc Phuong is a global centre for plant diversity and home to Delacour's Langur, a critically endangered primate, as well as the grey headed fish eagle, tigers and elephants.

The official said the committee had examined two options: to upgrade an existing road running through the west of the park into a 28 km (17 miles) stretch of highway, or to build a new road, skirting the park.

She said the latter road would be 20 km (12 miles) longer, cost nearly $20 million more and require the relocation of more than 900 families instead of 80.

The official said said the former plan included 3,200 metres (yards) of bridges to limit the environmental impact. However, she conceded that environmentals remained worried, saying: "They are concerned about many things, including the impact of the construction and of traffic running through the natural reserve."

The Ho Chi Minh Highway will be Vietnam's second national route linking the north and the south of the country. It will run 1,690 km (1,056 miles) from near Hanoi in the north to Ho Chi Minh City in the south.

It will follow parts of the legendary Ho Chi Minh Trail, a maze of jungle tracks used to move men and supplies from communist North Vietnam to U.S.-backed South Vietnam during the Vietnam War.

Monday's Vietnam Investment Review quoted Craig Leisher, a programme director of the World Wildlife Fund, as saying it recognised the need for a new highway but did not recommend building it through the park.