Five young Japanese were found dead inside a sealed van on Monday in an apparent group suicide, authorities said.

A passer-by discovered the bodies of the three men and two women, all believed to be in their twenties, slumped in the vehicle parked along the Yasu River in western Shiga prefecture on Monday, according to local police official Takao Higuchi.

Investigators found a charcoal stove in the van and suspect the group died of asphyxiation, Higuchi said. Charcoal stoves, which emit carbon monoxide fumes that cause asphyxia in sealed areas, are typically used in group suicides in Japan.

A note that read, simply, "Thank you" was also found in the van, according to public broadcaster NHK.

Click here for FOXNews.com's Asia center.

Police have yet to identify the bodies and do not yet know what the relationship is between the five, Higuchi said.

Japan has seen a spate of group suicides in recent years, many involving young people who meet on Internet chat sites and travel across Japan to kill themselves together in deserted places.

A record 91 people killed themselves in 34 Internet-linked suicide pacts in 2005, almost triple the number in 2003, when the National Police Agency started compiling statistics.

Often designed with an ominous, pitch-black background, the Internet sites spill over with death wishes and ideas on how best to commit suicide.

They appear to be frequented largely by young people, some still in their early teens, who are troubled by bullying, abusive relatives or a disconnect with society.

Politicians have suggested that suicide sites be regulated or shut down. But experts have said the crackdown has only driven suicidal people to use overseas providers, which are almost impossible to regulate.

Others argue that the sites, by allowing suicidal people to share their concerns, prevent more deaths than they facilitate.

Though shocking, Internet-related suicides still represent a small percentage of suicides in Japan. More than 32,500 Japanese took their own lives in 2005, the bulk of them older Japanese suffering from sickness or financial woes.

Click here for FOXNews.com's Asia center.