Another critical week for Prime Minister Yoshiro Mori began Monday with the Upper House approving the resignation of Masakuni Murakami, one of the embattled prime minister's staunch backers.

Murakami, formerly dubbed the Liberal Democratic Party's Upper House "guru," had his resignation unanimously approved at a plenary session in the morning.

Murakami submitted his resignation last week for "causing trouble" through his alleged ties with KSD, a mutual aid foundation at the heart of a widening bribery scandal.

In another move related to the widening scandal, Fukushiro Nukaga, former state minister for economic and fiscal policy, was grilled over his alleged involvement with KSD at a Lower House committee on political ethics the same day.

The latest development on the KSD scandal will likely erode Mori's already shaky foundation, and already potential replacements are lining up.

Speaking in Osaka, senior LDP member Taku Yamasaki expressed readiness to run in an LDP presidential election in the event Mori steps down, in a bid to ensure the selection process be conducted openly.

"If LDP executives pick a successor behind the closed door and nobody (else) stands, I will do it," said Yamasaki, a former chairman of the LDP's Policy Research Council.

At the closed-door House of Representatives ethics panel meeting, Nukaga denied any wrongdoing, including his involvement in putting the name of a Saitama college in the policy speech of then Prime Minister Keizo Obuchi. But he admitted that his secretary received a total of 15 million yen in cash from Tadao Koseki, former president of the scandal-tainted mutual-aid organization KSD, and apologized for causing a nuisance to the public.

The money was later returned to Koseki, who is under arrest on suspicion of bribery, he said.

"I feel I thoroughly explained that I was not involved (in the incident)," Nukaga told reporters after the council.

Nukaga resigned as state minister in charge of economic and fiscal policy and information technology Jan. 23 after being criticized over allegations he accepted the bribes.

Opposition lawmakers have accused Nukaga -- who was deputy Cabinet secretary at the time and helped draft Obuchi's speech -- of accepting the cash as a reward for mentioning the college in the speech.

"I have never been involved in the foundation of the university, nor have I ever been required to do anything for Koseki," Nukaga said. "And I have no idea how the name of the university was included in the speech."

According to Nukaga, he took part in a meeting to draft the policy speech on three occasions in January 2000. The name of the university was included in a draft of the speech in the third meeting, he said.

Following approval of Murakami's resignation at the Upper House session, Mori apologized, noting that the KSD incident has tarnished the public's trust in politics.

"I frankly regret this as the party's president and must offer apologies to the people," Mori told the Lower House Budget Committee.

Murakami, the second Diet member to resign over the KSD scandal, is one of five LDP elders who handpicked Mori to succeed former Prime Minister Keizo Obuchi, who suffered a stroke last April and died in May.

Takao Koyama, Murakami's former secretary, quit the Upper House shortly after his arrest on Jan. 16 on suspicion of accepting 20 million yen in bribes from KSD in 1996.

The LDP's Hideki Miyazaki, 69, will take over Murakami's seat.

Chief Cabinet Secretary Yasuo Fukuda said at a regular news conference that the government will "straighten things that need to be straightened" with Murakami's case constituting a starting point for this process.

Murakami, 68, the former head of LDP members in the House of Councilors, is expected to testify under oath Wednesday about his ties with KSD. The organization has allegedly given Murakami some 100 million yen, partly in return for political favors.

One allegation leveled against Murakami is that he helped KSD establish a new vocational university in Saitama Prefecture and helped it to obtain government subsidies.