SYDNEY/KUALA LUMPUR – Australia-listed rare earths miner Lynas Corp said on Monday that reports an opponent of its refinery in Malaysia will head a government review of the plant "raise concerns", as its shares lost nearly a quarter of their value.

Lynas is the only major miner outside China of the metallic elements, crucial in the production of magnets. It mines raw material in Western Australia which is sent to a plant in Malaysia for processing.

Malaysia's government, elected in an unexpected landslide in May, had previously flagged a review of concerns surrounding the refinery, which activists say is envionmentally hazardous.

On Friday the Star newspaper, citing a Ministerial letter of appointment, reported that Fuziah Salleh, a government politician and a long-time critic of the plant, will chair a committee reviewing the plant. She will lead it for three months, beginning Monday, the newspaper said.

Fuziah had no immediate response when contacted by Reuters.

Lynas said on Monday its operations had already been extensively scrutinised and that it will advocate for a "transparent, impartial and scientific" review.

"The media has speculated that the chair of the proposed committee may be a long time anti-Lynas campaigner. If that appointment is confirmed, then that will raise concerns," the company said in a statement, without specifying what they were.

Lynas shares fell 23% to A$1.61, their lowest since last September, in a slightly weaker broader market.

The strategic significance of rare earth metals was highlighted last week when the United States excluded them from a round of import tariffs.

Lynas' main products, neodymium and praseodymium, are used in magnets for motors that drive automated seats and windows in cars, motors for hybrid vehicles and as magnets in electronic products, like DVDs and hard disk drives.

Its $800-million plant, which produces low-level radioactive waste, began operations in 2012 after long delays caused by legal challenges and environmental disputes.