NTT Docomo Inc. plans to cut mobile phone fees across the board, sources familiar with the matter said, becoming the first of Japan's major carriers to do so following a government call for the industry to lower charges.

NTT Docomo said Wednesday it will hold a press conference on new service plans Thursday, at which it is expected to outline the details of the lower charges. The new service plans from Japan's leading mobile phone operator by subscribers could spark price competition in a market in which the three largest carriers, including KDDI Corp. and SoftBank Corp., control roughly 90 percent.

Prime Minister Yoshihide Suga has asked mobile phone carriers to slash fees, saying their charges are high compared with other countries.

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Prior to taking office in September, Suga said "healthy competition" was necessary and the three mobile phone companies should offer cheaper plans given their profit margins of around 20 percent that are higher than other infrastructure providers such as utilities.

KDDI and SoftBank have already said their budget brands will offer 20-gigabyte plans at lower prices of around 4,000 yen ($38) per month.

NTT Docomo is preparing to bolster its competitiveness by becoming a wholly owned unit of parent Nippon Telegraph and Telephone Corp by the end of the month.

The No. 1 mobile phone carrier plans to launch a low-cost brand like its domestic rivals and offer 20-gigabyte monthly plans at around 3,000 yen, the sources said.

But as Ryota Takeda, the telecommunications minister, has continued to demand that the top three bands cut fees, NTT Docomo plans to slash its own service plans as well.