A top Chinese diplomat says his country will not link Iran's nuclear program to trade.

The comments by Deputy Foreign Minister Cui Tiankai come on the eve of a visit to Beijing by U.S. Secretary of Treasury Timothy Geithner, in which he is expected to seek support for sanctions against Tehran.

Cui said Monday that the normal trade relations and energy cooperation between China and Iran have nothing to do with the nuclear issue. He said people should not mix issues with different natures. Cui also said China's legitimate concerns should be respected.

China is one of Iran's biggest markets for oil.

The U.S. Treasury Department said last week that Geithner will seek Chinese help in imposing financial measures against Iran, including the Central Bank of Iran, in an effort to force Tehran to abandon its nuclear development program.

The department said Geithner also will talk to Chinese officials about ways to promote global economic growth, and will bring up what it called measures to “level the playing field for U.S. workers and firms.”

U.S. officials have long contended that the Chinese currency, the yuan, is substantially undervalued. The U.S. says that gives Chinese exporters an unfair advantage and has led to a wide U.S. trade deficit with China.

Geithner travels to Beijing Tuesday for a meeting with Chinese Vice Premier Wang Qishan, and then will meet the following day with Premier Wen Jiabao, Vice President Xi Jinping and Executive Vice Premier Li Keqiang.

Geithner travels Thursday to Tokyo.

In November, the United States, Britain and Canada imposed additional sanctions on Iran, citing evidence that Iran is pursuing nuclear weapons. It is a contention that Tehran denies.