South Korea's health authorities said Wednesday they will announce the results of their investigation into possible harmful substances in heat-not-burn electronic cigarettes next month.

The Ministry of Food and Drug Safety said it will make its announcement before June 13.

The ministry launched the probe in August into three tobacco heating devices -- IQOS by Philip Morris Korea Inc., British American Tobacco's Glo and South Korean leading cigarette maker KT&G Corp.'s lil.