Police investigate the scene of the stabbing of a former health ministry official in Tokyo November 18, 2008. Japan's top health ministry and public pension officials were being warned about their personal safety after the suspected murder of a former vice minister and a stabbing at the home of another on Tuesday, the ministry said. [Agencies]

The suspected murder of a former vice health minister and the stabbing of the wife of another, both with careers tied to Japan's ailing pension system, prompted Japanese police to tighten security for officials on Wednesday.

The attacks follow a series of scandals involving pensions and health care for Japan's rapidly ageing population, including the mishandling of millions of pension records. The introduction of a medical insurance scheme that forced some elderly citizens to pay more also angered the public.

A former vice health minister and his wife were found dead at their home on Tuesday from what appeared to be multiple stab wounds, police said.

The wife of another former vice health minister was later stabbed at her home by a man disguising himself as a delivery man. Her wounds were not fatal.

"I don't know if the two incidents are linked, but it is heartbreaking," Prime Minister Taro Aso told reporters.

"I am praying for the souls of those who were killed and the recovery of the (official's wife) who was wounded."

The health ministry late on Tuesday alerted its top officials and gave the National Police Agency names and addresses of former senior officials so it could step up security around their homes.