The finance ministry is offering 1.1 trillion yen ($13.7 billion) of 20-year notes. "The auction will probably be tepid, not so strong but not so weak, but it might show decent demand since worries about Europe's economy remain," said a fund manager at a Japanese trust bank. Bond prices were supported by concerns about Greece's ability to stick to its austerity programme, and a slowdown in European growth after Markit's Eurozone Services Purchasing Managers' Index unexpectedly shrank. February is usually a big month for bond index duration extensions, so such appetite from pension funds could be stronger than last month and help the auction, Barclays Capital strategist Noriatsu Tanji said in a note. The yield on the 20-year note gained a basis point to 1.760 percent, while the thirty-year bond yield rose two points to 1.940 percent. The yield on the latest 10-year JGBs was flat at 0.975 percent. Ten-year JGB futures inched up 0.04 point to 142.51, with resistance seen at their 10-day moving average of 142.59. Concerns about the strength of Japan's economy underpinned bonds. A Reuters poll showed on Thursday that Japanese manufacturing sentiment in February slid to its lowest since the aftermath of the March 2011 earthquake, indicating the world's No.3 economy may struggle to recover quickly from a slump on weak global demand and a strong yen. Foreign investors marked their largest net selling of JGBs since June 2011 in the week through Feb. 18, finance ministry data released on Thursday showed. After two weeks of net buying, foreigners shed 661.7 billion yen worth of JGBs, while Japanese investors turned net sellers of foreign bonds for the first time in seven weeks.