Beijing yesterday joined a growing clamour of complaint about US plans for a carbon tax on imports from countries without their own emission caps, warning it could set off a global trade war.

The warning follows the passage of a cap-and-trade bill in the US House of Representatives last weekend, which contained tough provisions to impose carbon tariffs to ensure that American companies would not lose competitive advantage. A recent report by the World Trade Organisation and the UN said such taxes could in theory be crafted to be compatible with WTO law, but it would be hard to prove they were not an illegal disguised restriction on international trade.