Trade minister Akira Amari defended the government's move to delay its decision on a U.K. hedge fund's bid to double its stake in the nation's biggest wholesale power producer, citing national security.

The government extended the standard 30-day review until mid-May after Children's Investment Fund Management Ltd. in January sought permission to buy a 10 percent stake valued at ¥63.3 billion and raise its holding in Electric Power Development Co., known as J-Power, to 20 percent.

"J-Power is the only company that has an electricity-transmission network that connects all of Japan's islands, thereby affecting the lives of our citizens," Amari said in an interview broadcast Tuesday on Bloomberg Television. "It's only natural for Japan to extend the screening process."