U.S. Treasury Secretary Timothy Geithner and Chinese leaders pledged Wednesday to build economic ties but Beijing gave no sign it would relent in its opposition to American sanctions on Iran.

Geithner also planned to press Beijing on U.S. complaints about its currency controls as well as lobby for support in Washington's effort to rein in Iranian nuclear ambitions. China, a major buyer of Iranian crude, has rejected unilateral U.S. action as improper and industry analysts say it is unlikely to cooperate with an oil embargo.

The secretary and Chinese officials were upbeat about relations in portions of meetings reporters were allowed to watch and gave no sign of their conflicts.

"I believe your visit will go a long way to promote the stability and further growth of our economic relationship," said Vice President Xi Jinping, in line to be China's next leader.

Geithner replied that the two sides have a "very strong cooperative relationship" on global economic growth, nuclear nonproliferation and other issues.

"We are looking forward to building on that," he said.

Washington is targeting Iran's oil exports in an attempt to halt what Western governments say is its effort to develop nuclear weapons. The sanctions would bar financial institutions from the U.S. market if they do business with Iran's central bank.

China's fast-growing economy is the world's biggest energy consumer and depends on Iran for 11 percent of its oil imports. China bought about 600,000 barrels of Iranian crude per day in November, nearly one-third of Iran's daily exports of 2.2 million barrels, making Chinese cooperation key to the success of sanctions.

In a meeting Tuesday night with Geithner, Vice Premier Wang Qishan pledged cooperation on global economic issues and called on the United States to loosen export controls on high-tech goods, according to the official Xinhua News Agency. China has long objected to U.S. limits on sales of "dual use" technologies with possible military applications.

Geithner also met with Vice Premier Li Keqiang, another rising political star, and was due to meet Premier Wen Jiabao, the country's top economic official.

Wen is due to visit major oil producers Saudi Arabia, the United Arab Emirates and Qatar on a trip that starts this weekend.

Chinese officials have given no details of planned talks, but Wen would have a high-level opportunity to sound out possible alternative suppliers in case Beijing agrees to buy less Iranian crude.

Geithner's visit was overshadowed by tensions over Iran but comes amid U.S. frustration with China's currency controls and swollen trade surplus that Washington and other governments complain are hampering economic growth.

U.S. officials said Geithner would press Beijing to ease controls that Washington and other governments say keep its yuan undervalued and give its exporters an unfair price advantage _ a volatile issue at a time when the global economy is struggling and governments are under pressure to lower high unemployment.

The Chinese government reported Tuesday that its trade surplus with the United States swelled 24 percent in December over a year earlier to $17.4 billion.

Beijing has allowed the yuan to rise in recent years in tightly controlled trading but some American lawmakers are calling for punitive tariffs on Chinese goods if the communist government doesn't move faster.

Later Wednesday, Geithner was to fly to Japan, another major buyer of Iranian oil, to lobby for support for sanctions.

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Associated Press writer Alexa Olesen and researcher Zhao Liang contributed.