SHANGHAI, March 19 (Reuters) - China"s yuan weakened on Friday and was set for a fifth week of losses as the greenback gained ground and as Sino-U.S. tensions weighed. The People"s Bank of China (PBOC) set the midpoint rate at 6.5098 per dollar prior to the market open, 239 pips weaker than the previous fix of 6.4859. The spot market opened at 6.5130 per dollar and was changing hands at 6.5138 at midday, 78 pips lower than the previous late session close. If the yuan finishes the late night session at the midday level, it would post a weekly loss of 50 pips, its fifth straight week of declines. The offshore yuan was trading at 6.515 per dollar. The safe-haven U.S. dollar strengthened again on Friday, supported by higher Treasury yields and falling stock markets, as investors continued to digest the Federal Reserve"s pushback against expectations of any early interest-rate hikes. The benchmark U.S. 10-year yield climbed to a more than one-year peak of 1.754% overnight before easing to 1.715%, while Asian stocks followed Wall Street lower. Traders said the yield surge lifted the dollar and pressured the A-share market and the yuan, which could test a recent low hit on March 9. "The yuan"s appreciation increasingly loses momentum as the dollar index and the U.S. treasury yield rise," said a trader at Chinese bank. Dollar-denominated assets would become more attractive if their return rises faster than similar assets of other economies, CITIC Securities analysts said in a report. The U.S. 10-year yield is expected to rise back to 2% or higher sooner or later as long as the U.S. economy and inflation expectations are strong enough, the brokerage added. Adding to the pressure on the yuan were worries over Sino-U.S. tensions. The United States and China issued sharp rebukes of each others" policies in the first high-level, in-person talks of the Biden administration on Thursday, with deeply strained relations of the two global rivals on rare public display during the meeting"s opening session in Alaska. The Thomson Reuters/HKEX Global CNH index, which tracks the offshore yuan against a basket of currencies on a daily basis, stood at 96.72, flat with the previous day"s 96.72. The global dollar index rose to 91.861 from the previous close of 91.828. Offshore one-year non-deliverable forwards contracts (NDFs), considered the best available proxy for forward-looking market expectations of the yuan"s value, traded at 6.6975, 2.80 percent away from the midpoint. One-year NDFs are settled against the midpoint, not the spot rate. The yuan market at 3:40AM GMT: ONSHORE SPOT: Item Current Previous Change PBOC midpoint 6.5098 6.4859 -0.37% Spot yuan 6.5138 6.506 -0.12% Divergence from 0.06% midpoint* Spot change YTD 0.22% Spot change since 2005 27.06% revaluation Key indexes: Item Current Previous Change Thomson 96.72 96.72 0.0 Reuters/HKEX CNH index Dollar index 91.861 91.828 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 6.515 -0.02% * Offshore 6.6975 -2.80% 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 Luoyan Liu, Jindong Zhang and Andrew Galbraith; Editing by Kim Coghill)