China warned the United States on Thursday not to meddle in its trade relations with Iran after Washington expressed concern about a Chinese oil company's planned investment in an Iranian gas field.

"We think this kind of cooperation and relationship is legitimate. Normal cooperation should not be interfered (with)," said Chinese Foreign Ministry spokesman Liu Jianchao.

Asked if that meant Beijing believed the United States was interfering in its dealings with Iran, Liu said, "This is our position."

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The U.S. government expressed concern to Beijing last month about a planned investment by state-owned Chinese oil company CNOOC Ltd. in Iran's Northern Pars gas field. Washington said major business dealings with Tehran were inappropriate while Iran is defying U.N. resolutions on its nuclear program.

CNOOC spokesman Liu Junshan said Thursday the company was still in talks with the Iranian side to develop the gas field and to help build liquefied natural gas facilities. He said no agreement had yet been signed, and declined to estimate the project's value.

The Iranian Mehr news agency reported last month that the deal was worth US$16 billion (euro12 billion).

Liu's comments came as Israel's Prime Minister Ehud Olmert visited Beijing. Olmert is seeking a more proactive Chinese role in pressuring Iran to abandon its nuclear program.

Iran's president has called for Israel to be wiped off the face of the earth, and Iran is widely believed to be trying to manufacture atomic bombs — a charge it denies.

In talks with Olmert Wednesday, Chinese Premier Wen Jiabao said Beijing was firmly against nuclear weapons proliferation in Iran and wanted to see a diplomatic solution to the issue, Liu said at a press briefing.

But it is unlikely that Beijing will to bend to U.S. pressure to drop the gas deal, considering China's growing thirst for oil and gas to fuel its economic boom.

China imported 980 million barrels of oil last year, making it the world's third-biggest consumer of foreign oil. Its demand for natural gas is expected to rise 26 percent over the next five years.

China's two major oil companies — China Petrochemical Corp. and China National Petroleum Corp. — are both either involved in gas projects in Iran or in talks to participate in developing gas resources.

Iran has seen the lure of its energy resources and other markets as a way to weaken the willl of U.N. Security Council members to exact harsh punishment over its nuclear program, which Tehran claims is for generating electricity.

The council, of which China is one of five permanent members, voted last month to impose sanctions on Iran for refusing to abandon uranium enrichment — a process that produces the material for either nuclear reactors or bombs.