* Dollar/yen jumps above 85 yen then retreats
* Traders cite intervention talk but no confirmation
* Euro rises on IFO, resilient to sovereign debt problems
By Anirban Nag
LONDON, Sept 24 (Reuters) - The dollar spiked above 85.00 yen on Friday on talk of intervention by Japanese authorities keen to stem the yen's recent gains, but quickly retreated as doubts emerged about whether they had taken action.
That left investors nervous about more intervention and, with risk aversion hitting markets, traders said the Bank of Japan's task of weakening the yen was becoming even tougher.
The dollar rose as high as 85.40 yen JPY= from about 84.55 before talk of intervention emerged, climbing more than one yen from 84.34 yen. It later retreated to 84.26 yen, a one-week low and down 0.1 percent for the day.
"The price action certainly suggested that the Japanese intervened, but one can't be sure," said Kenneth Broux, markets strategist at Lloyds TSB Financial Markets.
"With stock markets retreating and a general pullback in risk appetite, the yen and the Swiss franc will be supported, making the BoJ's job harder."
Japanese officials stayed silent on whether they had intervened. Top currency diplomat Rintaro Tamaki declined to comment, Jiji news agency reported, and the Bank of Japan and the government also had no comment. [ID:nTKU106266].
Japan intervened for the first time in six years last week in repeated action that pushed the yen down from a 15-year high of 82.87 per dollar and shunted it above 85.
The dollar stayed above 85.00 yen until the Federal Reserve signalled this week that it might take more quantitative easing steps, putting widespread selling pressure on the greenback and casting doubt over how effective solo intervention can be.
"At these levels, one can expect the Japanese to intervene," said Lee Hardman, currency economist at BTM-UFJ. "Certainly the stronger fundamentals support a stronger yen, but I guess the Japanese authorities will be keen to draw a line in the sand."
UPWARD PRESSURE ON YEN AND EURO
The dollar's jump came after it had fallen to 84.26 yen on Thursday, its lowest since Japan intervened last week, and traders said major Japanese banks were bidding up the dollar.
"Rather than saying clearly whether they did or not, they may be trying to make market players jittery," said one Japanese brokerage trader in Tokyo, who thought Japan probably did intervene on Friday.
"They are probably changing their methods, with the aim of dampening dollar-selling interest," the trader said.
Some dealers speculated an apparent lack of complaint by U.S. President Barack Obama about last week's intervention when he met Japanese Prime Minister Naoto Kan late on Thursday was seen as tacit approval by Washington of Japan's action.
Obama, who urged Chinese premier Wen Jiabao to take more action on the yuan, did not mention currencies when he met Kan, Kyodo news agency reported.
For cross/yen graphic
For graphic on intervention
For Insider Link: link.reuters.com/syb35p
The dollar faced resistance at 85.66 yen, its 55-day moving average, which has acted like trendline resistance since June. Traders said there was options-related selling in dollar/yen with option expiries at 85 yen later on Friday to drive trade.
Some traders said a rumour Bank of Japan Governor Masaaki Shirakawa might resign also helped the dollar. The BOJ said there was no truth to the rumour. [ID:nTKU106269]
The greenback has been under pressure in part due to shrinking yield gaps between the dollar and the yen.
As the dollar weakened, the euro rose 0.5 percent to $1.3380 EUR=, helped by strong German IFO numbers and moving closer to a five-month high of $1.3441 struck on Wednesday. [ID:nBAE003827].
Euro/yen EURJPY=R also gained 0.7 percent to 113.06 yen, with the euro having jumped as high as 113.75 and proving resilient to lingering euro zone sovereign debt problems.
The euro was also firmer against the Swiss franc EURCHF=, rising 0.4 percent to 1.3168 francs, aided in part by talk that Nestle may increase its stake in L'Oreal. That was later denied.
(Additional reporting by Tokyo Forex team)