SEOUL, May 23 (Yonhap) -- A group of local civic organizations called on the nation's tax office Thursday to conduct a thorough investigation into users of overseas tax havens and take stern legal action against those who are found to be tax evaders. The call came a day after the independent association Korean Center for Investigative Journalism said more than 200 South Koreans used famous tax-heaven regions -- the Virgin and Cook Islands -- to stash secretive funds in suspected attempts to avoid taxes in their home country.