The yen moved past 160 per US dollar to its weakest level in a month, extending a slide that has erased more than half of its intervention-fueled gains, according to Bloomberg. The Japanese currency fell as much as 0.5% to 160.20 versus the greenback on Friday after the dollar got a boost from Federal Reserve Chairman Kevin Warsh's vow to hit the central bank's inflation target, with traders now watching for signs of when authorities might move to protect the currency. Hedge funds added to short yen bets for a second straight week, according to Commodity Futures Trading Commission data for the period ending Aug. 25.

The yen has been under pressure since failing to push through 155 earlier this month, in the wake of joint action on July 31 when the US and Japan conducted their first coordinated yen-buying intervention since 1998. The latest weakness came even after Treasury Secretary Scott Bessent made a fresh attempt to rein in long-term US borrowing costs from multi-year highs. Bank of America strategist Alex Cohen said intervention expectations will inevitably increase with the yen at the psychologically relevant 160 level, though authorities are likely to be more patient given the move is largely dollar- and US-rates-driven. Investors remain concerned about the wide rate gap between Japan and other economies, the country's heavy debt burden and rising oil prices.

State Street Investment Management's Masahiko Loo said the mid-160s is becoming a policy level rather than a valuation level, with Washington and Tokyo effectively drawing a political line in the sand, and did not rule out another round of intervention before a potential Bank of Japan hike as early as September. The BOJ meets next month, with markets pricing in about an 80% chance of a hike, while traders also expect a Fed rate increase this year. BNY strategist Geoffrey Yu said he expects Japanese authorities to hold off on intervention for now with the rates meeting approaching.

Prime Minister Sanae Takaichi's government is said to support a near-term BOJ hike given the yen weakness. The currency had been near a four-decade low of around 164 per dollar before the late-July intervention that saw the US join Japan in its defense, and authorities had also intervened in the summer of 2024 when the yen crossed the 160-per-dollar level.