The Bank of Japan owned a record 52.02% of outstanding Japanese government bonds at the end of December, as the central bank ramped up purchases to defend its cap on long-term yields, data showed Friday.

The BOJ's holdings came to ¥546.93 trillion ($4.1 trillion) while the total amount of outstanding government debt was at ¥1.05 quadrillion. The ownership level was an increase on three months earlier when it crossed the 50% mark for the first time, according to the BOJ data.

While the world's major central banks went ahead with aggressive interest rate hikes to fight inflation, higher overseas bond yields added upward pressure on the BOJ last year.