Police in the northern port city of Hai Phong Wednesday began investigating four members of a family on murder charges after six officers were shot injured in an encounter with them last week.

Under the decision issued by the city's police, Doan Van Vuon together with his two brothers, Doan Van Qui and Doan Van Sinh, and his nephew, Doan Van Ve, will be in custody during the investigation.

Meanwhile, Vuon's wife, Nguyen Thi Thuong, and Qui's wife, Pham Thi Hien, will be investigated on charges of "acting against people on public mission."

The local prosecutors' office will consider ratifying the charges.

According to police, two other members of the family, Doan Van Thoai, Vuon's younger brother, and Pham Van Thai, Hien's brother, are still at large.

On January 5, local police and military went to Vuon's home to force his family to return the 50-hectare land that Tien Lang District's authorities assigned to him for aquaculture farming for 14 years. His right to use the land expired in 2009.

However, the family refused and set up self-made mines along the only entrance to their house, which is also located on the land, to stop the forces.

During the confrontation, Qui, Thoai and Thai allegedly shot four policemen and two soldiers, injuring them with two self-made guns.

After that the trio fled the scene, while others along with Doan Xuan Quynh, 17-year-old son of Vuon, were arrested.

Thuong, Hien and Quynh were released later. Qui turned himself to police on January 8.

The case is being investigated further.