CHINA yesterday warned Washington of 'very serious' difficulties if Taiwan President Lee Teng-hui is re-elected in March and invited back to the United States. Chinese Foreign Minister Qian Qichen, speaking before meeting US Secretary of State Warren Christopher during the APEC summit, said Taiwan remained the most sensitive issue in Sino-US relations. A US visit by Mr Lee 'would be a very serious problem', said Mr Qian. 'However, I do not think this represents the position of the US Government.' When Taiwan was raised in his meeting with Mr Christopher, Mr Qian said the US should abide by the three communiques it had signed with China. However, the two apparently failed to make much ground on relations, merely reiterating they were willing to strengthen co-operation in areas agreed by presidents Bill Clinton and Jiang Zemin in New York last month. A spokesman for Mr Qian said China was ready to work more closely with the US in areas such as the economy and environmental protection. Mr Qian asked the US to honour its pledge to support China's accession to the World Trade Organisation. Mr Christopher said more talks were needed although Washington 'strongly supports' China's entry bid. He also said despite differences in areas like human rights, he hoped talks on these subjects would continue. They also agreed to improve co-operation on United Nations affairs and fighting drug trafficking and money laundering.