U.S. President Barack Obama on Tuesday warned China to stop limiting its exports of so-called “rare earth” minerals used to make high-technology products.

Mr. Obama described it as an unfair restriction of trade, saying, “Our competitors should be on notice: You will not get away 'with skirting the rules.'”

The United States, Japan and the 27-nation European Union joined forces Tuesday and filed a formal complaint against China with the World Trade Organization in Geneva to seek a resolution of the dispute. They alleged that China, which controls 95 percent of the world's supply of those minerals, has imposed export restrictions that violate world trade rules.

President Obama said he is pursuing the trade complaint so American companies can compete fairly against foreign businesses in the production of goods that require the use of the rare earths.

“Now if China would simply let the market work on its own, we'd have no objections. But their policies currently are preventing that from happening and they go against the very rules that China agreed to follow.”

China says it has restricted its export quotas in recent years in order to meet its own domestic manufacturing needs, and to address environmental concerns. Chinese officials also have rejected the charges of illegal activity.

But Patrick Chovanec, a professor at Beijing's Tsinghua University School of Economics and Management, told VOA that the WTO has already ruled against China in a similar case.

“The WTO ruled, in a ruling last year, regarding other raw materials, not rare earths but other similar raw materials, that if China wanted to conserve natural resources, or it wanted to protect the environment, that export constraints were not a legitimate way of doing so.”

Washington says the restrictions give Chinese companies an unfair advantage by increasing production costs for foreign firms, while Chovanec suggests Beijing is trying to force high-tech manufacturers to relocate their operations to China.

Chovanec said the Chinese restrictions have prompted other countries to begin scrambling for new sources of the materials.

“The reason why China has a monopoly isn't because it has a stranglehold on the supply, it's just that it's the lowest-cost producer and everyone else got out of the business. There are Australian companies, American companies, Japanese companies are looking around in Central Asia and other places and even on the ocean floor for these materials.”

The rare earth minerals are essential to the production of such common consumer items as flat-screen televisions, smartphones and hybrid cars, as well as advanced weaponry, small motors that raise and lower car windows, and wind turbines.

China says it adheres to WTO rules in exporting the minerals. But U.S. Trade Representative Ron Kirk said that China has reduced its export of the minerals in recent years, giving Chinese companies an unfair advantage in the production of high-technology products. He said China's export restraints result in massive distortions and harmful disruptions in the supply of the rare earths throughout the world.

Mr. Obama has also announced the creation of a new trade enforcement center to ensure that China and other nations abide by WTO rules.