Poison gas may have been abandoned at 138 sites in 41 prefectures at the end of World War II, according to the results of a nationwide study released Friday by the Environment Ministry.

"The government will consider appropriate measures to deal with (abandoned poison gas) as early as next month," Environment Minister Yuriko Koike told a regular news conference in response to the study results.

The ministry launched the probe in June, after a series of incidents in which health problems were linked to abandoned poison gas came to light.