* Euro tests 4-year peaks against yen, one-month top on US dollar
* Shanghai shares up, investors shrug off tensions over air zone
* Other Asian stock markets mixed, Japan pares losses
The euro reached fresh highs on both the yen and U.S. dollar on Wednesday, while Shanghai stocks shrugged off geopolitical concerns to outpace an otherwise lacklustre regional performance.
The single currency touched a four-year peak against the yen and a one-month high on the dollar as speculators wrestled with major chart resistance at 138.00 yen and $1.3600. A break here would likely open the way to further gains for euro bulls.
While most share markets were subdued after a flat finish on Wall Street, China's CSI300 of leading Shanghai and Shenzhen A-shares stood out with a 1.0 percent gain.
Investors there seemed unperturbed by the step up in tensions over Beijing's demands that airlines inform them when flying over disputed islands in the East China Sea, a move the White House termed "unnecessarily inflammatory."
The United States responded on Tuesday by flying two unarmed B-52 bombers over the region, while ANA and Japan Airlines stopped sending Chinese authorities their flight plans for routes that pass through the zone.
"It is bubbling away under the surface. In an environment where there's not a lot of data, then keeping one eye on geopolitics is probably going to be a good idea as well, because you never know what might come of that," said Sue Trinh, senior currency strategist at RBC Capital Markets in Hong Kong.
In truth there was no clear theme running through markets, except perhaps for a reluctance to get involved ahead of the U.S. Thanksgiving holiday on Thursday and next week's payrolls report.
Japan's Nikkei eased 0.3 percent to inch further away from the six-month peak touched on Monday. Conviction was equally lacking elsewhere, with MSCI's broadest index of Asia-Pacific shares outside Japan up 0.1 percent.
Wall Street had faded late on Tuesday after upbeat U.S. data on home building and house prices were offset by a disappointing reading on consumer confidence.
The Dow shed its early gains to end flat, while the S&P 500 Index eked out a 0.01 percent rise.
The Nasdaq managed to outperform thanks to gains in big-cap technology stocks and finished above 4,000 for the first time since the dot-com bubble burst in 2000.
Low for longer
In debt markets it was notable that investors continue to push out the date when the Federal Reserve might first raise official rates, proof the central bank has succeeded in divorcing tapering from tightening.
Eurodollar and Fed fund futures extended their three-month-old rally with many contracts reaching new highs. The market no longer has a first hike priced in until the very end of 2015, while before the Fed's September decision not to taper, it had been wagering on late 2014.
That sea change has in turn tempered the rise in longer-term rates with yields on 10-year Treasury paper slipping to 2.71 percent from a peak of 2.84 percent last week.
It might also be one reason the U.S. dollar is struggling against some of its major counterparts. The euro got as far as $1.3600 on Wednesday, its highest since Oct. 31.
The single currency also pushed above 138.00 yen for the first time in four years and looked to be heading for the 2009 peak around 139.18.
The gains have come even as a who's who of officials at the European Central Bank opened the door to more policy easing including a negative deposit rate.
The dollar has also lost altitude against sterling and the Swiss franc over the last couple of weeks.
In contrast the dollar has fared much better against the yen, thanks in part to the Bank of Japan's continued commitment to its massive asset-buying campaign. On Wednesday, the dollar was hovering at 101.56 yen just off the recent six-month peak around 101.91.
In commodities, U.S. crude oil was pressured after industry group American Petroleum Institute (API) reported a 6.9 million barrel rise in crude oil inventories, far higher than the 600,000-barrel build anticipated by analysts.
Nymex crude eased 21 cents to $93.47 a barrel, leaving it not far from five-month lows.
Brent crude oil futures was steadier at $110.95 a barrel as investors concluded that a deal between Iran and world powers would bring no immediate increase in crude supplies.