Telecommunications Minister Toranosuke Katayama said Tuesday he will urge Nippon Telegraph and Telephone Corp. to voluntarily craft and submit a business plan to increase competition among its group firms.

The plan should feature a reduction in NTT's equity stake in NTT DoCoMo Inc., the group's mobile phone giant, to less than 50 percent, said Katayama, minister of public management, home affairs, posts and telecommunications.

"We will demand that NTT volunteer to devise an action program (for inducing greater competition) as quickly as possible," he said.