Washington has banned imports of a key solar panel material from Chinese firm Hoshine Silicon Industry over allegations of forced labor.

That's according to Reuters sources.

The Commerce Department has also restricted exports to Hoshine, as well as three other companies and a paramilitary organisation.

At least some of the firms are major suppliers of silicon products used in solar panels.

The U.S. says they've all been involved in the use of forced labor by Uyghurs and other Muslim minority groups in China's Xinjiang province.

Beijing is accused of holding more than 1 million people camps there - allegations that China strongly denies.

The region accounts for about 45% of all the polysilicon used in solar modules.

That means restrictions could pose problems for the renewable energy industry.

Though experts say polysilicon can still be sourced from other parts of China.

None of the firms involved would comment on the reports.

A Chinese foreign ministry spokesman strongly condemned the U.S. move, and said Beijing would take all necessary steps to safeguard its firms.