Rep. Kwak Sang-do, an independent lawmaker who defected from the main opposition People Power Party a week ago, offered to resign from his parliamentary seat on Saturday amid mounting suspicions over his son receiving an unreasonably huge sum of severance pay from a firm at the center of a massive land development scandal.

"I can no longer work as a member of parliament amid widespread misunderstanding and distrust toward me," Kwak said in a news conference at the National Assembly.

"Everything regarding the nature of my son's severance pay and whether I was involved in the land development project (in Seongnam) and the relevant company will be revealed through investigations," he said, calling for a swift and thorough probe.'

Kwak left the People Power Party last Sunday after media reports revealed that his son received 5 billion won ($4.24 million) after some seven years of work at Hwacheon Daeyu Asset Management, the company suspected of reaping huge gains from the land development project in Seongnam, just south of Seoul, launched in 2015 when Gyeonggi Gov. Lee Jae-myung, currently a presidential front-runner for the ruling Democratic Party, was the city's major.

Kwak, a prosecutor-turned-politician elected twice to the Assembly from a district in the southeastern city of Daegu, had also served as the senior presidential secretary for civil affairs during the presidency of Park Geun-hye.

According to the National Assembly Act, a majority vote is required to approve a lawmaker's resignation.

Kwak's resignation offer came one day after a group of 51 lawmakers, mostly from the Democratic Party, submitted a motion to discipline him. A large number of People Power Party lawmakers have also stepped up pressure on him to resign.

Kwak is also under police investigations, as civic activists recently filed a criminal complaint against him on suspicions of bribery.

In recent days, prosecutors and police have been speeding up their investigations into the Seongnam land development scandal amid allegations that Lee gave business favors to certain developers during his days as the city's mayor years ago. (Yonhap)