Three Japanese men were found dead in a car Monday in what police suspect is the latest in a string of suicides using lethal gas made from household detergent.

The three, in their 20s and 30s, were found by a passer-by in Tomioka north of Tokyo, said police spokesman Tominori Hirata. The car was in a parking lot.

"We found bottles of bath and toilet detergent in the car," Hirata said, adding that police suspect the trio committed suicide by inhaling hydrogen sulfide gas made with the cleaning chemicals — a method that reportedly claimed more than 50 lives in Japan in April alone. Hirata declined to give further details.

Kyodo News agency said police found a warning sign outside the car reading, "Hydrogen sulfide gas being emitted."

Alarmed by a wave of similar incidents, Japanese police have launched a crackdown on popular Internet sites that give instructions on how to commit suicide by inhaling hydrogen sulfide made by mixing common household products.

Authorities also fear the deadly gas could endanger bystanders or rescuers. Earlier this month a man killed himself by mixing detergent in his house on the northern island of Hokkaido, releasing toxic fumes that drove 350 neighbors from their homes.

The government said 32,155 people killed themselves in Japan in 2006, giving the country the world's ninth highest suicide rate.

The government has earmarked $220 million for anti-suicide programs to help those with depression and other mental conditions.