The World Trade Organization yesterday opened an investigation into United States import taxes on Chinese tires.

The dispute focuses on a three-year tariff approved in September by US President Barack Obama and is the latest in a string of trade battles between the two countries.

China told the WTO that the United States had broken a vow it has made to avoid protectionism.

At a meeting of trade diplomats, US official Juan Millan expressed Washington's disappointment in the new case.

The US blocked China's request last month for a tire probe, but could not do so a second time under WTO rules.

The arbitrators will evaluate whether the US tariffs violate rules governing trade among the WTO's 153 members. Trade cases often take years to resolve, but can result in the WTO authorizing retaliatory sanctions.

Obama ordered the higher tire tariffs for three years, including a 35 percent additional charge in the first year. It comes on top of a regular 4 percent tariff.

Tires imported from China are low-end models. While American-made, name-brand tires can easily cost more than US$100 each, Chinese imports sometimes sell for half that. The tariffs would make them more expensive.

China notes that its tire exports to the United States fell by about 15 percent in the first half of last year, and says two in three tires exported to the US are made by Chinese-foreign joint ventures. This means American companies are also profiting from the trade.

The US imported 46 million tires from China in 2008.