BOSTON - The United States and China should address their currency issue "cooperatively," says the director of the US National Economic Council.

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A sharp adjustment of the exchange rate will not serve China or the United States but tensions between the two countries would accumulate if the mark remains unchanged, Lawrence Summers said Sunday at the Harvard-China Small- and Medium-Sized Enterprises Conference.

"It will be the task of our governments to navigate in this turbulent water," said Summers, who is also a former president of Harvard University.

Summers said he was encouraged by the recent appreciation of the Chinese yuan and expected the trend to continue in the near future.

Talking about China's enormous holding of US treasury bonds, Summers said he believed "borrowers have the responsibility" for their debts.

"If I borrow too much money and am not be able to pay the credit card company back, I think I should be blamed, not the credit card company," he said.

Both Americans and Chinese benefit from bilateral trade, Summers said. The two countries need to trade and exchange much more in the future and promote their commercial ties, he said.