KDDI Corp, Japan's second-largest mobile carrier by subscribers, has snagged the rights to sell Apple's iPhone 5, a report said Thursday, in a blow to its rival Softbank.

Threatening the market dominance enjoyed by Softbank as Apple's only partner in Japan, the US computer giant and KDDI have already agreed on a sales deal for the highly-anticipated phone, the Nikkei business newspaper reported in its online edition, citing unnamed sources.

But KDDI will need a few months to prepare for the roll-out of iPhone 5 and will not be ready in October when Apple is expected to launch the new model around the world - including in Japan through Softbank, the report said.

A KDDI spokesman declined to comment on the report.

Softbank, Japan's third-largest mobile carrier by subscribers, has so far enjoyed a monopoly on the hugely popular iPhone and iPad as Apple's only carrier in Japan.

The Nikkei report sent Softbank shares plunging 12.29 percent to 2,282 yen, while KDDI closed down 0.79 percent at 624,000 after giving up earlier gains.

Apple ended its exclusive alliance with AT&T in the United States in February when it allowed iPhones synched to Verizon's network to hit the market.