Some players said JGBs could remain firm as investors fret that unrest in the Middle East and North Africa could lift oil prices more and derail global economic growth.

"JGBs gained as more domestic participants are feeling safe about entering the market again after a bear run that started in January. The events in the Middle East are favouring debt as they could hurt the economy and stocks," said a trader at a European brokerage.

"But as far as we can see the events in the Middle East are yet to spur a massive flight into JGBs by foreign investors looking for a safe-haven."

March 10-year futures were up 0.09 point at 139.79 after hitting a three-week high of 139.82.

The 20-year yield fell 2 basis points to 1.995 percent, with longer-dated maturities supported by index following players' month-end purchases, traders said.

The benchmark 10-year yield dropped 2 basis points to 1.220 percent, its lowest in three weeks. The yield rose to a 10-month peak of 1.350 percent earlier this month before the unrest in the Middle East escalated.

The five-year yield was down 0.5 basis point at 0.525 percent.

"Bond yields come under upward pressures in an inflationary environment, but we don't know how long the unrest in the Middle East and the region will continue, so investors are likely to keep buying bonds on safe-haven demand," said Katsutoshi Inadome, a fixed-income strategist at Mitsubishi UFJ Morgan Stanley Securities.

The market's reaction was limited after an auction of two-year bonds on Thursday drew mediocre demand. It attracted bids 3.70 times the amount accepted, down from 5.33 at the previous sale.

Still, analysts expect the market to eventually absorb the new offer amid ample funding by the BOJ.

JGBs kept gains after Moody's warning on Tuesday that it may cut Japan's sovereign debt rating. The JGB market has been taking credit rating cuts in stride over the past decade.

The head of Japan's public pension fund (GPIF), the world's largest, said on Wednesday the fund's investment strategy will not be affected by downgrades of Japanese government bonds by credit ratings agencies.

However, he also said that Japan's bulging public debt -- the largest among developed countries at double the size of its economy -- would reach a crucial point in five to 10 years if the problem is not resolved.

US Treasury yields rose on Wednesday as investors prepared for a seven-year note sale on Thursday, overcoming a safe-haven bid for government debt as Middle East tensions sent oil prices higher and weighed on stocks.