SEOUL - South Korean President Lee Myung-bak's only son was summoned Thursday for questioning over allegations of irregularities in a land deal.

"I will explain everything as it is," Lee's 34-year-old son Si-hyung told reporters before entering the office of the special counsel re-investigating the case that could potentially implicate the president.

Last year, the junior Lee and the presidential security service jointly bought 462 square meters of land in an affluent neighborhood in southern Seoul to build the president's retirement residence.

The plot was purchased in Si-hyung's name, a violation of South Korea's real estate law that prompted allegations of real estate speculation and tax evasion.

The junior Lee is also suspected of purchasing the land at a below-market price by letting the security service pay more.

The retirement home scandal drew public criticism, prodding Lee to scrap his plan, though prosecutors who initially probed the case acquitted everyone involved in the deal, including Si-hyung.

The case marks the first time a child of an incumbent leader has been summoned as a suspect. Lee's five-year term ends early next year.

The independent counsel, recommended by the opposition Democratic United Party, can conduct the probe for up to 45 days.