Police found two women dead and one man in critical condition Monday afternoon inside a car in a mountainous part of Awaji, Hyogo Prefecture, apparently victims of a group suicide attempt.
The women were both in their 20s, local policeman Yoshikazu Murata said.
The car's windows had been sealed with tape and a used charcoal stove was found inside the vehicle, suggesting the victims succumbed to carbon monoxide poisoning, Murata said.
A man, also in his 20s, was rushed to a hospital but remained unconscious, he added. Authorities had yet to identify the three.
There has been a recent spate of group suicides arranged by strangers communicating to each other over the Internet -- though it wasn't immediately clear how the latest group met.
This month alone, 13 people have been found dead in three separate Internet-linked group suicides, excluding the latest case.
On March 10, six people were found dead in a van in a forested area outside of Tokyo. Police suspect the six -- from different parts of Japan -- met in an Internet chat room.
Internet suicide pacts have occurred since at least the late 1990s, and have been reported in a number of countries. But in Japan, where the suicide rate is among the industrialized world's highest, officials are particularly worried about the trend.
A record 91 people died in 34 Internet-linked group suicides 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.
Though shocking, Internet-related suicides still represent a small percentage of the nation's suicides. More than 32,000 people took their own lives in 2004.