KDDI Corp. said Thursday it is considering lowering mobile phone fees following a decision to cut charges by its bigger rival NTT Docomo Inc., as mobile phone carriers face government pressure to slash rates.

"We will take proactive measures to lower fees and simplify our fee plans," KDDI President Makoto Takahashi told a press conference in Tokyo.

In August, Chief Cabinet Secretary Yoshihide Suga said that mobile phone charges in Japan should be cut by 40 percent, while the Ministry of Internal Affairs and Communications recently set up a panel to discuss mobile phone fees.

"I'd like the carriers to make their services available to users with reasonable charges," Suga told a press conference after the news that KDDI was considering lowering fees.

Some surveys have shown mobile phone fees in Japan are higher than in other countries, and the top Japanese carriers including SoftBank Corp. have been criticized for using long-term contracts and complicated service agreements to lock in subscribers.

NTT Docomo, Japan's largest mobile carrier, said Wednesday it will slash its cellphone charges by 20 to 40 percent from the April-June quarter next year. Takahashi said KDDI will not try to match the fee cuts by NTT Docomo.

The charge cuts by NTT Docomo and KDDI are expected to push SoftBank Corp. to cut its fees.

The share prices of the three mobile phone carriers plunged Thursday on the Tokyo Stock Exchange due to concern that stiffer competition would significantly hurt their profitability. KDDI tumbled 16.1 percent, NTT Docomo 14.7 percent and SoftBank Group 8.2 percent.

KDDI also said it will form a business alliance with e-commerce giant Rakuten Inc., which was granted approval by the government in April to enter the mobile phone market currently dominated by the three major mobile companies.

KDDI will lease its communication systems for Rakuten's mobile phone service to be launched next year, while Rakuten will help KDDI strengthen online shopping and smartphone settlement.