A local consumer advocacy group said Monday it plans to ask prosecutors to investigate SK Group Chairman Chey Tae-won and his mistress over alleged wrongdoings related to their property deal.

The woman, a U.S. citizen identified by her surname Kim, bought a luxury apartment in southern Seoul for 1.55 billion won in 2008, and then sold it to the Singapore-based consulting firm Bergaya International for 2.4 billion won two years later.

The apartment was built by the group's construction arm of SK E&C, and the consulting company is an affiliate of SK Singapore.

"We will request the prosecution this week to open a probe into possible violations of local laws regarding the suspected real estate transaction," the Seoul-based Financial Consumer Agency said.

A thorough probe into any unethical and unlawful actions by an owner of a conglomerate should be carried out to bring them to justice, it added.

The woman is suspected of breaching the Foreign Exchange Transactions Act as she failed to report the deal to the Bank of Korea.

Last week, the Financial Supervisory Service, the nation's financial watchdog, started a probe into the deal.

The forex deal act stipulates that non-residents shall inform the central bank of any real estate transactions in Korea.

The consumer group also plans to seek a probe into Chey over speculation that he might have embezzled corporate funds to purchase the house for Kim via the overseas affiliate.

The apartment deal has come under media spotlight since late last year when the chairman admitted that he is in an extramarital relationship with the woman while going through divorce proceedings with his wife. (Yonhap)