The World Trade Organization strengthened its support Thursday for China in a final ruling in a dispute over punitive duties imposed by the United States on a range of Chinese products.

A WTO appellate body upheld a panel ruling from July that Washington had "acted inconsistently" with global rules when it imposed extra import duties on a number of Chinese products.

The United States has slapped additional tariffs on products ranging from paper to tyres, magnets, chemicals, kitchen fittings and solar panels, arguing they were being dumped on its market to help Chinese companies grab business.

The July ruling charged that the US duties had "nullified or impaired benefits accruing to China".

"We recommend that the United States bring its measures into conformity with its obligations," that ruling added.

China said at the time that the annual export value of the affected products was around $7.2 billion.

Thursday's appeals body ruling went even further in its support for China.

It slapped down an appeal by the United States charging that China's initial complaint and request to set up a panel on the issue in 2012 was inconsistent with WTO rules.

Responding to an appeal by China, it also reversed the few findings by the panel that had sided with the US in July.

The WTO polices global trade accords in an effort to provide its 160 member economies with a level playing field.

Members have the right to impose extra duties when goods are being "dumped" on them or sold at below market prices to corner a share of business unfairly.

But hand in hand with that right, they are obliged to prove that their domestic producers are suffering as a result of dumping, and that the duties are not simply being deployed to protect them against foreign competitors.

Wrangling over dumping is common at the WTO, whose panels can authorise retaliatory trade measures against a guilty party that fails to fall into line.

Thursday's ruling cannot be appealed.