TOKYO, Dec 24 (IFR) - Japanese government bonds were mostly steady on Wednesday, with trading volumes in both cash and futures markets thin ahead of the long Christmas holiday weekend in the U.S. and Europe.

The Bank of Japan refrained from offering to buy JGBs under its asset purchase programme. Market participants now expect the central bank to buy 400 billion yen ($3.32 billion) of JGBs maturing in more than 5 years and within 10 years on Friday and next Monday, and not offer to purchase superlong JGBs in the remaining days of December.

A sharp rise in U.S. Treasury yields overnight after the sharp upward revision of U.S. July-September growth figures had limited negative impact on JGBs.

At midday, the 10-year yield was flat at 0.335 percent, compared with 0.340 percent earlier in the session, while the 20-year yield was also steady at 1.10 percent.

The yield on the current 2-year JGBs edged up 0.5 basis point from Monday to minus 0.03 percent ahead of Thursday's monthly 2.7 trillion yen 2-year JGB auction, while the 5-year yield added 1 basis point to 0.045 percent.

Lead 10-year March JGB futures were flat at 147.70.

($1 = 120.3900 yen) (Reporting by Masatsugu Hisatsune; Editing by Shri Navaratnam)