The justice ministry has approved a request from investigators to impose a travel ban on the former head of the National Election Commission (NEC) amid a probe into shortages of ballots during last week's local elections, sources said Friday. The ministry took the measure against Roh Tae-ak, former chairperson of the NEC, as well as other key officials upon requests made by a team of investigators probing the case, according to judiciary sources. The move came a day after investigators conducted