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The benchmark Nikkei stock average was down 0.2% at 14,167.83 as of 0155 GMT, trading below its 25-day moving average of 14,391.77.
Analysts said trading volume may stay low as investors stay wary towards developments in Ukraine amid fears the country is sliding into civil war. Pro-Moscow rebels on Sunday declared a resounding victory in a referendum on self-rule for eastern Ukraine.
"We may have more concerns than reasons to be optimistic about the market until June, when the prime minister (Shinzo Abe) is scheduled to flesh out the details of the growth strategy," said Takuya Takahashi, a strategist at Daiwa Securities.
Takahashi added that individual earnings can set the direction of the market for the time being.
DeNA Co tumbled 21 percent to 1,287 yen - its lowest since November 2009 - and was the second-most traded stock by turnover, after the smartphone gaming producer said it expects a big decline in its sales and profits for the April-June quarter.
But Olympus soared as much as 4.9 percent to a one-week high after forecasting a 19.8 percent rise in operating profit to 88 billion yen for the year ending in March 2015. The figure was below the median forecast of 94.4 billion yen in a Thomson Reuters Starmine poll of 17 analysts. But traders said the company's forecast is seen as too conservative given that it is aiming to strengthen its profitable medical business.
Exporters weakened as the dollar stayed below 102 yen.
Toyota Motor Corp fell 0.5%, Sony Corp shed 0.2% and Nikon Corp dropped 0.4%.
The broader Topix shed 0.3% to 1,162.37, while the new JPX-Nikkei Index 400 dropped 0.3% to 10,576.31.
