The Labour Ministry's permanent secretary Chuthatawat Indrasuksri will launch the probe, the source said. Former Social Security Office (SSO) secretary-general Pairote Sooksamrit, now serving as the ministry's deputy permanent secretary, reportedly inked the deal even before an inspection of the building was completed.

SSO deputy secretary-general Thanachon Suriyanakangkura was also named as another key official behind the deal, the source said. "An investigation panel has pointed out that even though the deal has been aborted, the SSO suffered some financial damage," the source said.

The inquiry panel is one of six established to investigate controversial projects at the SSO.

Alleged irregularities were also found in SSO schemes to provide dental-care and child-delivery assistance to members of social networks, the source added.

Meanwhile, a panel looking into SSO investments in stock markets overseas has asked for another month to complete its inquiry. Some stock options chosen were suspicious and had caused the Social Security Fund to suffer losses, the source said.