Barack Obama, the US president, has said his administration will take a firmer stance with China on enforcing trade rules, ramping up the tone in a relationship that has shown signs of becoming increasingly strained.
His comments at a meeting on Wednesday with members of his Democratic party come amid tensions between the two countries over a recent arms sale to Taiwan an upcoming visit to the US by the Dalai Lama, and a row over alleged cyber attacks against internet search giant Google.
Speaking to Democrats Obama said that he supported trade agreements with China but urged Beijing to open its markets to more US goods.
"The approach that we are taking is to try to get much tougher about enforcement of existing rules," he said.
He added that what was needed was "putting constant pressure on China and other countries to open up their markets in reciprocal ways".
Obama also hinted that the strength of China's currency, the yuan, remains a divisive issue amid growing anger in the US Congress over the country's monetary policy.
Many Western policymakers accuse China of keeping the yuan artificially low for the benefit of its manufacturing industry, funding a flow of cheap exports around the world and causing job losses in firms unable to compete.
US politicians from both major parties have accused Obama and George Bush, his predecessor, of being soft on China by refusing to declare it a currency manipulator.
However, analysts say that Obama's comments are predominantly aimed at appealing to a domestic audience rather than to seriously put pressure on Beijing.
The Chinese government has repeatedly stated that its exchange rate policy is an internal matter, and has warned the US against falling prey to protectionist sentiment.
Obama's message of a tougher stance with Beijing comes against a background of growing strains in Sino-US ties, particularly over Beijing's repeated warnings against the US president meeting the Dalai Lama.
|China has warned of "severe consequences" over the US-Taiwan arms sale [Reuters]
The exiled Tibetan spiritual leader is due to visit the US later this month and on Tuesday White House officials confirmed that he would meet Obama, although where and when has yet to be announced.
That has infuriated Beijing with Chinese officials saying that that Hu Jintao, the Chinese president, urged Obama not to meet the exiled Tibetan leader during a summit in Beijing in November.
Ma Zhaoxu, a foreign ministry spokesman, told reporters on Wednesday that Hu had "explained China's stern position of resolutely opposing any government leaders and officials meeting the Dalai."
"We urge the US to fully grasp the high sensitivity of the Tibetan issues, to prudently and appropriately deal with related matters, and avoid bringing further damage to
Further fuelling Sino-US tensions is a recent announcement that the US has agreed to $6.4bn weapons package for Taiwan, the self-ruled island that China views as a renegade province.
Tensions over cyber security and control of the internet have also soured ties.
Internet giant Google said last month that would no longer follow Chinese internet censorship laws and may pull out of the country altogether after it uncovered a "sophisticated" computer attack on the email accounts of human rights activists protesting against Chinese policies.
Hillary Clinton, the US secretary of state, called on China to investigate the alleged cyber attacks in a "transparent" manner and said countries restricting free access to information risked "walling themselves off from the progress of the next century".