At least four people, including three police officers, were killed in Vietnam on Thursday when protesters attacked authorities trying to build a wall near a military airport, the Ministry of Public Security said.

The protesters attacked the authorities with hand grenades, petrol bombs and knives in Dong Tam village, near the capital, Hanoi, the ministry said in a statement on its website.

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Three policemen and one of the protesters were killed, while another protester was injured, the ministry said.

It did not elaborate on the protesters' objections.

"The authorities have launched an investigation into the case and have arrested the lawbreakers," the ministry said.

Disputes over land do occur in Vietnam. However, it was the first time in years when policemen were killed in such a dispute.