Donald Trump has ordered a 15% tariff on imported products made with polysilicon, a highly purified silicon used in solar panels and semiconductors. The measure, due to take effect on 4 December, is intended to strengthen US supply chains and reduce reliance on China, which is the main producer, amid competition over artificial intelligence, energy and national security.

The order also sets minimum import prices, including $21 (£15.62) per kilogram for polysilicon and $0.38 per watt for solar modules. US producers welcomed the move, while China said it was protectionist and harmful to trade; the Commerce Department may also introduce incentives for companies investing in US polysilicon production.