South Korea's state auditor is expected to conduct a special probe as early as later this month to determine the cause behind the frequent malfunctions involving the country's high-speed trains, an official source said Monday.

The source said Board of Audit and Inspection (BAI) chairman Yang Kun stressed at a meeting of senior officials that there is a need for a full and detailed examination into stoppages involving the Korea Train Express (KTX) trains.

The trains have been cited for stopping more than 30 times this year due to mechanical problems. They have drawn fire for their unreliability and triggered safety concerns among passengers.

"The chairman said the problems were taking place too frequently, and there is a need to start a probe as soon as possible," the source said, adding that the BAI plans to carry out a comprehensive review of how the trains are made, their overall operations and all of their problems discovered so far.

The comments follow a KTX train stopping for an hour inside the Hwangak Tunnel, about 240 kilometers southeast of Seoul, on Sunday.

About 400 people were stranded inside the train.

The KTX trains cited for experiencing the most problems have been the locally built versions of the original French TGV bullet trains. These trains are called the KTX-2 or the "KTX-Sancheon" by their operator, the state-run Korea Railroad Corp. (KORAIL).

Initially, the audit board had considered expanding a probe planned for later in the year, but it decided to speed up the process to alleviate worries.

"Mechanical, electrical and communications experts from both within and outside the BAI will be assigned to checking the KTX and KORAIL," the source said.

He added that while it is possible to start an audit by late July, delays can occur since there is a need to determine what areas need to be examined the most. (Yonhap News)