The on-site inquiry marks a far cry from the watchdog's normal probes into banks, which call for them to submit necessary data.

"Inspectors carried out the on-site investigations since a usual document-based examination makes it hard to detect hiring-related irregularities perpetrated clandestinely," an FSS official said.

Indeed, affected banks have reported to the watchdog that internal probes have found no evidence of wrongdoing in their hiring processes.

The watchdog has reportedly detected several cases of hiring irregularities involving children of former and incumbent bank executives, while planning to refer some of them to the prosecution for further investigation.

Meanwhile, the FSS itself has been under criticism after state auditors discovered in September that senior officials at the service gave special treatment to some job candidates related to politicians or senior financial executives.

In October, the government launched a probe into all state-funded companies to find out if undue preference was given to children of influential people in politics and business circles amid rising public anger over reports of hiring irregularities. (Yonhap)