TOKYO, April 21 (Reuters) - Japan's 10-year government bond yields remained at the upper limit of the Bank of Japan's target in early trade on Thursday, even after the central bank offered to buy unlimited amounts of the bonds.

The central bank will purchase unlimited amounts of the bonds from Thursday to Tuesday next week to keep the 10-year JGB from rising above the implicit 0.25% cap it sets around its 0% target.

The central bank boosted its defence on Wednesday after its single-day operation failed to lower the benchmark yields.

The 10-year JGBs were not traded and the yield stayed at 0.250%.

Yields on other notes retreated, with the 20-year JGB yield falling 1.5 basis points to 0.760%.

The 30-year JGB yield fell 1.5 basis points to 0.965%. The 40-year JGB yield fell 1 basis point to 1.055%.

The five-year yield fell 1.5 basis points to 0.015%. The two-year JGBs were not traded and the yield stayed at minus 0.050%. (Reporting by Junko Fujita; Editing by Subhranshu Sahu)