Forced to quit after barely a week as Japan's reconstruction minister for remarks deemed offensive to victims of the March earthquake and tsunami, Ryu Matsumoto had an unusual explanation for his behavior -- his blood type.

"My blood's type B, which means I can be irritable and impetuous, and my intentions don't always come across," he said Tuesday after his resignation.

"My wife called me earlier to point that out. I think I need to reflect about that."

Matsumoto was tapping into a widespread belief in Japan that blood types correspond to various character traits.

Japan's fascination with blood types began in the early 20th century and is similar to the belief in astrology and horoscopes. Many Japanese believe their blood type can foretell success in romance and the suitability for jobs.

It's not uncommon for the subject to come up in conversation, sometimes as explanation for an action, and a directory of members of parliament lists the blood types of many, along with their home towns and hobbies.

Many Japanese, however, said it was not an acceptable reason for Matsumoto's behavior on a trip to the devastated northern region, during which he told a prefecture governor the government would not help communities that failed to come up with ideas to help themselves.

Speaking before TV cameras, Matsumoto reprimanded the governor for keeping him waiting and then ordered journalists not to report the exchange or else their media outlets would suffer.

People with type B blood are believed to be stubborn, impulsive and cold, although they are also seen as practical, and Matsumoto's explanation was greeted with derision.

"He should apologize to all other Type Bs," said one user of a Web chat forum.

Matsumoto's resignation delivered a fresh blow to unpopular Prime Minister Naoto Kan, who is a blood type O -- believed to be sociable and energetic but flighty, able to easily start projects but then give them up just as fast.

(Read by Nelly Min. Nelly Min is a journalist at the China Daily Website.)