The yen weakened past the key 160-per-dollar level as it extends a slide that’s erased more than half of its intervention-fueled gains. The Japanese currency slipped as much as 0.5% to 160.16 versus the greenback after the dollar got a boost from Federal Reserve Chairman Kevin Warsh’s vow to hit the central bank’s inflation target. Traders now are carefully watching yen levels for signs of when authorities might move to protect the currency.

Japan Yen Intervention: Back Forward Currencies Facebook Linked In Gift Expand Japanese 10,000 yen and 5,000 yen banknotes. Photographer: Noriko Hayashi/Bloomberg.