Dollar-yen fell sharply and may be attempting to break below the 155 level for a third time. According to Sina Finance, yen option volumes this week are higher than in May and August, which is boosting foreign-exchange traders' confidence in their bets.

The pair came close to breaking that level in the previous two months but failed to do so. According to Sina Finance, this time the move is part of a broad rally, with trading volume in yen crosses against the euro and Swiss franc also significantly above normal.

According to Sina Finance, Japan's central bank is said to favor a 25-basis-point rate hike in two weeks rather than a larger move. Investors are increasingly viewing back-to-back rate hikes for the first time this century as a possible policy option, while the market is also pricing in a growing chance that the Federal Reserve will keep rates unchanged in September.