The two attacks are likely linked because former vice ministers were targeted in both attacks, according to a deputy chief who requesting anonymity as is often customary with Japanese police officials.

The Health Ministry has asked police to beef up security at local pension offices, where people go to claim their pensions and file complaints, including many elderly people.

'We are taking extra caution because we cannot rule out the possibility that the attacks are linked to the pension problem,' Health Minister Yoichi Masuzoe said on Friday on nationally televised news.

'We must not allow any attacks at pension offices, where many elderly people visit.'

Many Japanese - from politicians to pundits - are pointing the finger at widespread anger over the disappearance of 64 million records from the government pension system, a debacle that stripped many of their retirement funds.

Both of the targeted officials were retired vice health ministers who were key figures in setting up the pension system 20 years ago.

In response to the attacks, Japan placed dozens of senior Health Ministry officials under heavy security.

For days the Japanese media, TV commentators and other experts have said the culprit may be venting frustration over the problems in the pension system.

The Yomiuri, the nation's largest daily, noted in an editorial Wednesday: 'It is true that slipshod handling of pension records and dissatisfaction against the system have emerged as serious problems. Still, no matter the reason, terrorism should not be condoned.'

Former Nagasaki Mayor Hitoshi Motoshima, himself a victim of a 1990 assassination attempt, also pointed to anger over the pension mess.

'But it's out of the question to resort to violence in venting dissatisfaction about health policies,' Mr Motoshima wrote in Thursday's nationally circulated Asahi newspaper.

The Health Ministry has been inundated with angry e-mail and telephone calls blaming the pension fiasco for the stabbings, and the number of complaints about the scandal itself have shot up after the attacks, according to ministry official Akihiko Nagata.

Mr Nagata said on Friday some of the complaints were being handed over to the authorities with the possibility that they may have come from the culprit.

It is still unclear whether the attacker was the same in both cases, but police have noted similarities in the crimes. In both instances, the assailants posed as delivery men and visited the officials at home.

Takehiko Yamaguchi, 66, a former ministry bureaucrat, and his wife Michiko, 61, were found dead on Tuesday in their house in a tranquil middle-class Tokyo suburb. Hours later, the 72-year-old wife of a former vice health minister was stabbed and wounded. Her husband, Mr Kenji Yoshihara, was not home at the time.

Mr Ken Kitashiba, a criminology expert and former police detective, said that some Japanese extremists, including those with mob ties, have carried out attacks they feel are tied to public sentiments.

'These are the kind of people who have their own sense of heroism in sending a symbolic message,' Mr Kitashiba told The Associated Press. -- AP