China, which is locked in a dispute with major trading partners over its control of rare earth minerals, on Thursday announced additional export quotas for this year.

The Ministry of Commerce said it would allow companies to potentially export an additional 10,680 tonnes of rare earths, bringing the total for this year to 21,226 tonnes.

The United States, European Union and Japan lodged a complaint with the World Trade Organization in March, saying China was choking off exports of rare earths to unfairly benefit domestic industries.

China, a producer of more than 95 percent of the world's rare earths, which are used in high-tech equipment from iPods to missiles, has set output caps and export quotas on the coveted resource.

Beijing has defended its practices, saying they aim to protect resources and the environment in an effort to promote sustainable development.

The ministry said the additional quotas were given to 12 companies that had recently passed environmental checks, according to a statement. They included a subsidiary of aluminium maker Chalco.

The ministry in December last year granted its first batch of 2012 export quotas totalling 10,546 tonnes for 11 companies.

The government has previously said its total export quotas for the sought-after commodities would remain roughly the same this year as in 2011.

China granted two batches of rare earth export quotas totaling more than 30,000 tonnes last year.

The quotas give companies the opportunity to export, but they are not necessarily used, due to factors such as weak market conditions.