China has defended its curbs on rare earths mining and exports after a World Trade Organisation (WTO) challenge brought by the United States, Europe and Japan.

The government said on Wednesday that its controls were meant to protect the environment and preserve dwindling resources and were in line with its WTO free-trade commitments.

China accounts for most of the world’s production of rare earths, which are used in mobile phones and other high-tech products.

Global manufacturers were alarmed when China announced it would limit exports while trying to build its own industry to manufacture products that use rare earths.

“All the measures taken by the government aim at protecting resources and the eco-environment,” the government said in a statement issued with a report on its rare earths policies.

“They are in line with the international practice and relevant regulations of the WTO.”

The United States, the European Union and Japan filed complaints in March with the WTO charging that China was limiting its export of rare earths.

China accounts for more than 90 per cent of global production of 17 rare earth minerals that are used to make goods including hybrid cars, weapons, flat-screen TVs, mobile phones and camera lenses.

China has cut export quotas while it tries to build its own industry to manufacture lightweight magnets and other products made with rare earths.

Senior US administration officials have said Beijing’s export restrictions give Chinese companies an advantage by giving them access to more rare earths at a cheaper price.

China has about 30 per cent of global rare earths deposits.

The United States, Canada, Australia and other countries also have rare earths but most mining stopped in the 1990s as lower-cost Chinese ores came on the market.