Prime Minister Yoshiro Mori on Wednesday dismissed demands from the opposition that an investigation be launched into allegations that Hidenao Nakagawa, his former chief Cabinet secretary, leaked police information to warn his alleged mistress that she was going to be the target of a drugs bust.

"It would be very dangerous if I was able to issue a specific instruction to police to investigate" Nakagawa's case, Mori said, suggesting that the prime minister should not intervene in police operations.

He made the remark in a one-on-one debate with Yukio Hatoyama, head of the Democratic Party of Japan, in the day's Upper House session.

Mori said the police must be democratically controlled and politically neutral, citing Article 4 and Article 5 of the Police Law, which stipulates that the National Public Safety Commission is in charge of police operations.

Mori's remarks came in response to Hatoyama's demand that the prime minister himself look into the allegations, which last Friday forced his right-hand man to step down.

Hatoyama cited a tape recording -- aired in television programs on the eve of Nakagawa's resignation -- of a 1995 telephone conversation in which the lawmaker is heard warning a woman that she may be the subject of a drug investigation.

Mori replied, "I believe Mr. Nakagawa will clarify the truth to protect his honor as a politician."

Nakagawa, Mori's closest aide, has effectively admitted to having an extramarital affair but has denied leaking confidential police information to the woman, saying that what he conveyed to her was merely rumors.

Tetsuzo Fuwa, chairman of the Japanese Communist Party, questioned Mori's responsibility for Nakagawa's appointment, saying Nakagawa's major weakness was exploited "by a senior member of a rightist group."

Fuwa was referring to Nakagawa's alleged ties with a leading figure of a Tokyo-based rightist group, who reportedly blackmailed the lawmaker over his affair.

While Mori said he does not believe Nakagawa was linked to the figure, he added, "It was Mr. Nakagawa who was being blackmailed." He did not elaborate.

During the same Diet session, Takako Doi, leader of the Social Democratic Party, criticized Mori's Liberal Democratic Party for the dubious flow of funds to the party from the scandal-tainted mutual aid society KSD.

Doi said small and medium-size business owners who had taken part in KSD's mutual aid schemes were practically swindled of their money.

KSD allegedly misappropriated funds by donating through an affiliate a total of 130 million yen to the LDP's Tokyo branch.

Doi said the business owners paid the money to KSD for use in mutual aid programs, not to be donated to a specific political party. He said the LDP should repay the money.

Mori dodged the criticism, saying that the KSD affiliate, which has properly submitted reports on political donations, was considered a legitimate organization aimed at supporting small and medium-size firms.