* Exporters mixed after dollar-yen edges lower
* Nintendo tumbles on profit-taking
TOKYO, Sept 5 (Reuters) - Japan's Nikkei share average fell to a one-week low in choppy trade on Tuesday morning as geopolitical tensions over North Korea sapped risk appetite, while index-heavyweight Fast Retailing Co dropped on weak sales.
The Nikkei shed 0.4 percent to 19,431.02 in midmorning trade, after initially opening slightly higher. It fell to as low as 19,392.31, the weakest level since Aug. 29.
The United States accused North Korea's trading partners on Monday of aiding its nuclear ambitions and said Pyongyang was "begging for war" after the North's powerful nuclear test on Sunday and signs that further missile launches were on the way.
"It's natural that investors stay on the sidelines while fears about North Korea still linger," said Takuya Takahashi, a strategist at Daiwa Securities.
He also said that investors are focused on U.S. monetary policy and upcoming discussions over the U.S. debt ceiling, which will likely keep activity subdued for the time being.
Fast Retailing, the operator of Uniqlo clothing outlets, fell 1 percent after its domestic same-store sales slipped 3.4 percent in August from a year earlier.
Exporters were mixed after the dollar edged down 0.2 percent to 109.52 yen during Asian trade. It slid to 109.220 the previous day in a knee-jerk reaction to North Korea's nuclear bomb test on Sunday.
Toyota Motor Corp and Honda Motor Co rose 0.5 percent, while Hitachi Ltd fell 0.4 percent and Hoya Corp declined 1.8 percent.
Nintendo Co was down 2.7 percent on profit-taking, moving away from a 3-1/2 week high hit last Friday.
The Mothers market of start-up shares stumbled 4.6 percent to hit a more than four-month low.
The broader Topix shed 0.5 percent to 1,595.59 and the JPX-Nikkei Index 400 dropped 0.4 percent to 14,152.79. (Editing by Sam Holmes)