BEIJING (Reuters) - China’s rare earth exports in September fell 17.9% from August, customs data showed on Monday, amid lingering fears that the world’s top producer of the minerals will restrict supply because of its trade row with the United States.

China, the world’s largest rare earth exporter, sold 3,571 tonnes of rare earths in September, figures from the General Administration of Customs of China showed.

This was down from 4,352 tonnes in August. The volumes also fell 27.9% from 4,950 tonnes in September 2018.

China has raised the prospect of limiting rare earth exports to the United States in retaliation for U.S. tariffs, although it has not publicly announced any restrictions.

U.S. Commerce Secretary Wilbur Ross went last week on an official visit to Australia, home to Lynas Corp LYC.AX, the only major rare earths producer outside of China, as Washington seeks to shore up alternative sources of supply.

In the first nine months of 2019, China’s rare earth exports, which can fluctuate widely, came in at 36,398 tonnes, down 9% from the same period last year.