The SNB had foreign currency reserves of 254 billion Swiss francs, according to preliminary data it distributes to the International Monetary Fund. It had 232 billion Swiss francs in November.

The SNB was not immediately available for comment on the figures.

The SNB set a cap on the franc of 1.20 on Sept. 6, vowing unlimited currency interventions if needed to prevent it strengthening beyond that level.

The SNB has been using foreign exchange swaps and other measures to boost liquidity in the money market to weaken the franc.