OSAKA -- Yet another former senior official at the Kinki Postal Administration Office has been arrested on suspicion of using his position to urge postmasters to support the campaign of newly elected House of Councilors lawmaker Kenji Koso, police said.

The Monday evening arrest of Hiromasa Akai, 59, a former general affairs department chief at the office, brought to 15 the number of people arrested on suspicion of election violations connected to Koso, who ran on the ruling Liberal Democratic Party ticket in last month's Upper House election.

On Tuesday, posts minister Toranosuke Katayama said he would assemble top officials from regional posts bureaus and postal inspection bureaus to directly question them about the widening scandal and the roles, if any, they may have played during the Upper House race.