Yen stuck in twilight zone

Key developments that could influence markets on Friday:

• France: July inflation data
• EU: Q2 employment and GDP data

The yen is back in the intervention zone, but its fate now appears to rest with the Fed's policy path and hopes of aggressive hikes from the Bank of Japan, after a joint operation with the U.S. failed to stem the fragile currency's decline.

The currency is on track for its worst week in three months, hovering at 159.37 per U.S. dollar, inching ever closer to the crucial 160 level that could trigger another bout of intervention.

Tokyo spent billions propping up the yen in April-May and with the U.S. at the end of July. It has repeatedly said it stands ready to intervene again if needed.

And yet, the yen's weakness has persisted, mainly because of the interest rate difference between Japan and other major currencies. The math has not shifted enough.

The 10-year U.S. Treasury still yields close to 4.7%, versus under 2.9% for 10-year Japanese government bonds JP10YTN=JBTC. That gap is wide enough to keep the carry trade chugging along no matter how many billions of dollars get thrown at defending the yen.

So markets are now wagering it is the Bank of Japan's turn to help stem the yen's decline, with traders betting on a faster pace of hikes from a central bank that some analysts say has been fairly slow in increasing interest rates.

"Most market players believe the BOJ will raise rates in September and I think it should," said Tokyo's former top currency diplomat Mitsuhiro Furusawa, but added that what is more crucial is for the central bank to communicate is the likelihood of a faster pace of hikes.