HANOI (Reuters) -Police in Vietnam have arrested six people accused of violating mining regulations, including the chairman of a company at the heart of efforts to develop Vietnam's rare earth industry, seizing 13,715 tons of rare earths ores.

Among those arrested was Luu Anh Tuan, chairman of Vietnam Rare Earth JSC (VTRE), who was accused of forging value added tax receipts in trading rare earths with Thai Duong Group, which operates a mine in the northern Vietnamese province of Yen Bai, the Ministry of Public Security said on Friday.

VTRE has partnered with Australian mining companies Australian Strategic Materials (ASM) and Blackstone Minerals LTD, which were not involved in the investigation.

Blackstone had agreed to partner with VTRE to win concessions at the country's biggest mine, Dong Pao in Lai Chau province, it said in a public statement in September.

A Blackstone executive had told Reuters its investment in the project would amount to about $100 million should it win the tender, which it expected to be launched later this year.

ASM signed a binding agreement in April with VTRE for the purchase of 100 tons of processed rare earths this year, and committed to negotiating a longer-term supply deal.

Calls to Tuan went unanswered on Friday. VTRE's office in Hanoi has been shut for days, one person at the building said.

Asked about whether their deals would continue, the two Australian companies did not immediately respond to a request for comment. The Australian embassy in Hanoi declined to comment.

Doan Van Huan, chairman of Thai Duong Group, was also arrested, accused of illegally making 632 billion dong ($25.80 million) from the sales of ore extracted from its mine in Yen Bai province.

Calls to Thai Duong Group went unanswered on Friday.

Vietnam is planning to organise auctions for concessions at its largely unexploited rare earths mines, which are considered to contain the world's second biggest deposits of the critical minerals used in electric cars and wind turbines.

(Reporting by Khanh Vu and Francesco Guarascio; Editing by Edmund Klamann, Martin Petty)