Six bodies — five men and one woman in their 20s — were discovered early Friday in a car in Chichibu, about 50 miles northwest of Tokyo, said Ichiro Fukumoto, a spokesman with Chichibu police.
Fukumoto said three charcoal burners were still smoking in the car when the bodies were found, and the windows had been sealed with tape. Authorities thought the six met over the Internet before dying together in a forested area Thursday night.
A separate group of three bodies — one man and two women — was discovered Wednesday in Aomori, 360 miles northeast of Tokyo, a police official said on condition of anonymity because of department rules.
The three, in their 20s and 30s, also died by inhaling charcoal fumes in a car. Kyodo News agency reported they had met in a hospital and had told others they wanted to die.
Their deaths were the latest in a rash of group suicides in Japan, particularly those set up between strangers over the Internet.
A record 91 people died in 34 Internet-linked suicide cases last year, up from 55 people in 19 cases in 2004, the National Police Agency reported last month. The number of Internet suicide pacts has almost tripled from 2003, when the agency started keeping records.
Suicide pacts have been made over the Internet since at least the late 1990s, and have been reported everywhere from Guam to the Netherlands.
But especially large numbers have occurred in Japan, where suicide rates are among the world's highest. More than 32,000 Japanese took their own lives in 2004.