The top bureaucrat at the internal affairs ministry quit Friday for leaking administrative penalty information to Japan Post Holdings Co., which is under fire over improper sales of insurance products, the ministry said.

Shigeki Suzuki, vice minister at the ministry, resigned after the ministry decided to suspend him for three months for leaking a draft plan of the penalty it was set to impose on Japan Post, the former state-owned postal and financial services group which was privatized in 2007.

"The conduct constitutes an act that hurts trust and the neutrality of official duties, and it's extremely disappointing. I offer an apology," Sanae Takaichi, minister of internal affairs and communications, said at a press conference.

Takaichi added she will voluntarily return three months of her salary over the matter.

The ministry, which supervises the postal group, said Suzuki admitted to leaking the information by phone to Yasuo Suzuki, senior executive vice president of Japan Post and a former vice minister at the ministry.

It had launched an internal probe after finding that Suzuki knew about part of the discussions held at the ministry about ways to punish the company, two of whose subsidiaries submitted this month a report on their improper insurance sales.

Japan Post only said it is still confirming facts.

Japan Post Holdings said Wednesday its probe uncovered more than 12,836 cases of insurance product sales suspected of violating a law or in-house rules at the two subsidiaries, Japan Post Insurance Co. and Japan Post Co., in the five years through March this year.

Japan Post, 57 percent owned by the government, sells insurance products at over 20,000 post offices nationwide.

The ministry is set to announce the administrative penalty by the year-end.

The Financial Services Agency is separately considering issuance of an order to halt some business at the subsidiaries, sources close to the matter said earlier.