SHANGHAI, Sept 13 (Reuters) - China"s yuan eased off one-week highs against the dollar hit in the previous session, as renewed concerns over U.S.-China relations and doubts about the Chinese currency"s recent strength prompted some investors to buy dollars. Prior to market opening, the People"s Bank of China (PBOC) set the midpoint at 6.4497 per dollar, 69 pips firmer than the previous fix of 6.4566, the strongest since June 18. In the spot market, onshore yuan opened at 6.4500 per dollar and was changing hands at 6.4529 at midday, 89 pips weaker than the previous late session close. The spot yuan surged to a high of 6.4363 on Friday, the firmest since Sept. 3. The yuan has mostly traded between 6.45 and 6.5 per dollar over the past three months, but traders said a breach of the psychologically critical 6.45 threshold in the midpoint and spot rate prompted dollar purchases from corporate clients and banks" proprietary accounts. The yuan gained last week buoyed by signs of willingness to get U.S.-China relations back on track after President Joe Biden and President Xi Jinping discussed the need to manage competition between their countries and avoid conflict. But some traders said it remained too early to decide if gains in the yuan would be sustainable. "Although senior officials from China and the United States maintained communications this year, we have yet to see signs of substantial relief such as the lowering of tariffs," said Li Liuyang, chief currency analyst at China Merchants Bank. A trader at a foreign bank said huge uncertainty remains around geopolitical tensions and the health of the world"s second-largest economy. He added that last week"s phone call between Biden and Xi lifted market sentiment, but without solid improvements in either Sino-U.S. relations or Chinese economic fundamentals, the yuan would be unlikely to test a new trading range. Rocky relations between Beijing and Washington have been among the key factors influencing the yuan since the trade war began in 2018, eventually leading to tariffs from both sides. Meanwhile, data on Friday showed new bank lending in China rose less than expected in August from a nine-month low seen in July, raising speculation over whether more stimulus was needed to shore up slowing economic growth. By midday, the global dollar index rose to 92.659 from the previous close of 92.63, while offshore yuan was trading 0.06% away from the onshore spot at 6.4489 per dollar. The yuan market at 0403 GMT: ONSHORE SPOT: Item Current Previous Change PBOC midpoint 6.4497 6.4566 0.11% Spot yuan 6.4529 6.444 -0.14% Divergence from 0.05% midpoint* Spot change YTD 1.17% Spot change since 2005 28.26% revaluation Key indexes: Item Current Previous Change Thomson 98.95 99 -0.1 Reuters/HKEX CNH index Dollar index 92.659 92.63 0.0 *Divergence of the dollar/yuan exchange rate. Negative number indicates that spot yuan is trading stronger than the midpoint. The People"s Bank of China (PBOC) allows the exchange rate to rise or fall 2% from official midpoint rate it sets each morning. OFFSHORE CNH MARKET Instrument Current Difference from onshore Offshore spot yuan 6.4489 0.06% * Offshore 6.6299 -2.72% non-deliverable forwards ** *Premium for offshore spot over onshore **Figure reflects difference from PBOC"s official midpoint, since non-deliverable forwards are settled against the midpoint. . (Reporting by Winni Zhou and Andrew Galbraith; Editing by Jacqueline Wong)