"Doing this seriously damages the cooperative relations that the two sides have built,'' Wang said.
 
Asked at a news conference in Beijing how China would respond formally to the complaint, Wang said diplomats were still studying it.
 
He gave no direct response when asked to confirm reports that Chinese officials were planning a multibillion-dollar buying mission to the United States in connection with May trade talks.
 
Instead Wang said only that Beijing was "actively preparing" for the meeting, which he described as part of a high-level "strategic economic dialogue."
 
Surplus slides
 
China's trade surplus dipped
sharply in March [AP]
 
Earlier news reports said China plans to buy at least $12.5bn worth of US goods in an apparent attempt to ease tensions over its soaring trade surpluses.
 
US politicians are threatening to take action against China if it fails to ease currency controls that critics say are driving up its trade surplus.
 
Wang also said a sharp drop in China's trade surplus in March might have been due to changes in tax policies that encouraged exporters to ship goods earlier.
 
"This is one possible factor," he said, but added that the ministry had to do more research.
 
On Tuesday the Chinese government said that its March trade surplus fell sharply to $6.9bn, down from $23.7bn in February.
 
But economists said the dip probably was due to exporters shipping goods early ahead of a possible cut in tax rebates, and they said higher surpluses should continue.