Two men and a woman were found dead Thursday morning in a truck in Yamanashi Prefecture in another apparent case of group suicide, police said.
Police said a passerby found the three around 9 a.m. The truck was parked on a forest road in the town of Mitama.
A charcoal stove was found in the vehicle, which was sealed from inside with adhesive tape. The three apparently died of carbon monoxide poisoning.
The identities of the victims — believed to be in their 20s or 30s — were not immediately known.
The incident is the latest in a series of multiple suicides involving young people who use charcoal to induce carbon monoxide poisoning. Some of these suicides involved people who met via Internet suicide Web sites.
Suicide pacts have been made over the Internet since the late 1990s, and have been reported everywhere from Guam to the Netherlands. Experts say they tend to occur in cycles, with news of group suicides sparking copycat incidents.