Lieutenant General To An Xo, spokesman for the Ministry of Public Security, said Thu has been detained for prosecution.
The arrest comes as the latest development after the police expand investigation into illegal sand mining in the Mekong Delta province.
Thu had instructed Nguyen Viet Tri, director of the province's Department of Natural Resources and Environment, to enable Trung Hau 68 Company to exploit more sand than it has received a permit for.
For this, the company paid him VND1.2 billion.
The police have already launched an investigation into Tri also for "taking bribes" and seven other officials for "abusing authority while on duty."
Le Quang Binh, CEO of Trung Hau 68, and Vo Truyen Thong, deputy CEO, are being investigated for "violating rules in exploring and exploiting natural resources" and "giving bribes."
According to the police, the company was issued a license to mine 1.5 million cubic meters of sand to supply for the construction of four sections of the North-South Expressway.
But by the time the investigation began, the company had already mined more than 4.7 million cubic meters of sand valued at VND253 billion on the market.
Binh told the police that he shared part of the money earned from selling the sand with several officials, including the director of the environment department.