A government team investigating alleged speculation in the public sector has summoned a former head of a state agency that oversees construction in South Korea's central administrative city of Sejong.

The National Office of Investigation(NIO) under the Korean National Police Agency(KNPA) on Friday began questioning the former chief of the National Agency for Administrative City Construction.

While in the post in April 2017, the ex-official purchased over two-thousand square meters of land in Sejong under his wife's name. The land's appraised value jumped over 40 percent in three years from January 2017.

After stepping down in November that year, the ex-official bought another plot of land and a steel structure on it in Sejong, near an area selected for a state industrial project.

The former chief is the highest level official to be summoned in the NIO's ongoing investigation that involved a raid of the agency in question, Sejong City Hall and the state-run Korea Land and Housing Corporation(LH) a month ago.

Meanwhile, investigators have also conducted a raid on one of five lawmakers suspected of speculation. They, however, did not reveal the lawmaker's identity or party affiliation.