Prosecutors raided the offices of Samsung Group's affiliates on Thursday as part of an ongoing probe into alleged accounting fraud by its biopharmaceutical unit, Samsung BioLogics Co.

The raids come after the Financial Services Commission ruled that Samsung BioLogics intentionally violated accounting rules ahead of its initial public offering in 2016. The case has been referred to the prosecution.

The regulatory review centers on questions about the loss-making Samsung BioLogics' reporting of sudden profits in 2015 after changing the method used to calculate the value of Samsung Bioepis, a joint venture with US-based Biogen Inc.

Investigators from the Seoul Central District Prosecutors' Office searched the offices of Samsung C&T Corp, the group's key unit, and the data center of Samsung SDS Co., Samsung's IT service provider.

The raids come three and a half months after the prosecution office launched a probe into the snowballing allegations.

The financial regulator has judged that Samsung BioLogics' suspected fraudulent accounting possibly amounts to 4.5 trillion won ($4.35 billion).

The alleged irregularities helped boost the value of Cheil Industries and benefited Samsung Group's heir apparent, Lee Jae-yong, as Cheil Industries held a 46.3 percent stake in Samsung BioLogics and Lee was a major stakeholder in Cheil at that time, according to some ruling party lawmakers and civic groups.

The 2015 merger of Cheil and Samsung C&T was widely seen as a step to enhance Lee's control of Samsung Group, as his father Lee Kun-hee suffered a heart attack in 2014 and has been hospitalized ever since.

Samsung BioLogics has denied any wrongdoing, claiming that the change in accounting methods was in line with international accounting standards. It has also lodged an administrative suit in objection to the FSC decision. (Yonhap)