The Bank of Japan conducted an emergency bond purchase on Wednesday, offering to buy more bonds than at their previous unscheduled operation, but failed to stop Japanese government bond yields from climbing to fresh decade highs.

The benchmark 10-year JGB yield rose to 1.805% for the first time since August 2013, after the BOJ offered to buy an additional ?675 billion ($4.52 billion) worth of bonds with maturities between five and 10 years.

The central bank had announced on Monday that it would conduct the previously unscheduled bond-buying operation after the 10-year yield hit its highest in a decade that day.

¡°The BOJ offered to buy much more 10-year bonds than the market had expected but the effect was very limited,¡± said Kazuhiko Sano, a strategist at Tokai Tokyo Securities.

The 20-year yield jumped 6 basis points to 1.58%, a level not seen since December 2013, while the five-year ticked up to 0.34%, more than a decade-high.

The BOJ also announced offers for their regularly scheduled purchases of other maturities. The amount remained unchanged.

The bond-buying operation comes as speculation circulates about whether Japanese authorities intervened in the currency market overnight after the yen briefly weakened to ?150 against the dollar.

¡°With the yen falling to this level and growing speculation of the BOJ¡¯s policy tweak, it¡¯s hard to turn the momentum of rising yields around,¡± said Sano.

Yields have been rising globally, with U.S. Treasury yields reaching new 16-year highs during the day in Asia amid worries that the U.S. Federal Reserve will hold interest rates higher for longer.

In contrast, the BOJ has yet to exit from its ultraloose monetary policy, although anticipation has grown for a policy shift. The two-year JGB yield hit a multi-year high of 0.06% during the afternoon in Asia.

The 30-year JGB yield sat at a fresh 10-year high of 1.815% ahead of an auction on Thursday for the bond.